Better paintball equipment makes a better player
Although many experienced players will be quick to tell you that "it's not the gun, it's the player" it is still a common misconception that to be a better player you have to have better equipment. It is true that better equipment can make a given task easier on a player, but the skill necessary to be a successful player does not come in a box along with a new gun. I once saw a guy go from a Spyder, to an Automag RT, to a Shocker in the course of a few months looking for that "edge" which would let him compete. He incorrectly assumed it was all about how much paint can be shot in the quickest amount of time. He also incorrectly blamed his lack of on-field success on his perceived "inferior" equipment.  His problem, however, was that he had only been playing for that same few months. He lacked the experience to know what to do in certain situations, to know how to read the field, to know when and how to move, and to know how to work with his teammates in an effective manner. I don't think he plays anymore.
Steve Davidson writes:  Better paintball equipment makes a better player:  We have all seen the player who tries to 'buy game', and we all know the story that it's the player, not the gun.  On the other hand, something you failed to point out is that better equipment makes a good player more effective;  those of us who talked about good equipment were referring to improving the abilities of already experienced players.

Closed-bolt guns are inherently more accurate than open bolt guns
There is absolutely no definitive proof that closed-bolt paintball guns offer inherent design advantages over open-bolt guns, but there is plenty of evidence to the contrary. There are a number of theories and reasons why this myth sounds like it should be true, but a lot of those are based on firearms principles which are not necessarily applicable to paintball. The so-called "ball at rest before it's fired" theory would only apply if the gun is fired in a single shot fashion. During rapid firing, the difference, if there was any, would be null. At the same time, firing an open-bolt gun in single shot fashion can also produce better results in both accuracy and range (no shoot-down). What can be said for closed-bolt paintball guns is that they generally operate smoother than open-bolt guns (especially blow-backs) and they are therefore easier to hold on target while firing a successive string of shots. I own both open and closed-bolt guns which use the same barrels, and from my personal observations, using the same barrel and paint, there is no noticeable difference in accuracy.

Pumps have inherently better accuracy/range than Semi-automatics
Here's a statement that will piss off a lot of people: A Spyder with a good barrel and good paint will shoot every bit as good as a Phantom. How do I know? Because over the past 12 years, I have owned 4 Phantoms and 4 Spyders, not mention over 30 other assorted pumps and semi-automatics. Being a big fan of pump play, it would be real nice to sit here and say that pumps are more accurate or have more range - but it's just not true. The myth does have some basis in reality. When semi-autos appeared in the early 90's, they could not compete with the high end pumps of the day for consistency in accuracy or range. After all, semi-auto play was the new wave and most manufacturers were in a race to develop some kind of product, regardless of the overall performance, which generally suffered because the technology was in it's infancy. Meanwhile, high end pump manufacturer's had a decade's head start refining their products for a very competitive market. But things have long since changed.  Today's semi-autos benefit from from a decade of competition which forced a better product.  The myth that pumps perform better continues largely due to the fact that people who play with pumps are forced to play better and make their shots counts in order to compete with semi-automatics on the field.
Steve Davidson writes: Pump guns are more accurate than semis;  you correctly identified the fact that early semis were poor performers and that many years later the tech is now up to par;  however, you completely overlooked the influence that the heavier, larger paint from 'back in the day' had on range and accuracy;  Bob Long actually had some of the old paint replicated by Bullseye with his Ironball paint, which was a full 70 caliber in size.  Paint has generally reduced in size over the years and the vast majority of field or practice paint now mikes in at around 64/65 caliber;  using THAT paint through an older pump would tend to create the myth that pump guns were entirely inaccurate.

Longer barrels shoot better/with more accuracy
Again, this is an attempt to apply firearms principles where they don't necessarily apply. On rifled firearm barrels, more length can equate to more spin, a more stable trajectory, etc. Paintball gun barrels aren't really even barrels in the same sense, and would probably be more properly termed "launch tubes" (which I think Glen Palmer has referred to them as..) For paintball guns, the barrel only needs to be long enough to allow the ball to accelerate up to speed. What actual length of barrel works best is determined by valve timing and operating pressure of the particular gun. Any length beyond what is needed to get the ball to speed only provides added friction, which slows the ball down. In other words, a barrel that's too long will have to have more gas to overcome the friction effect to accelerate the ball up to a given speed, making that barrel less efficient.
 

Sights are useless in paintball
Despite what some people think, not everybody plays speedball where it's just one big slugfest and you don't have time to use a sight. I run into situations all of the time where I get the drop on an opponent and want my first shot to hit the target (especially when using a pump gun). I have been playing this game for a dozen years and have used sights successfully through the whole period. This myth comes from the fact that in today's game, most people shoot buckets of paintballs and simply watch where the balls go, correcting as needed (water hose effect). While I too use this method when conditions warrant, it doesn't mean I don't like having a sight on my gun. A good shooting paintball gun may not have pinpoint accuracy, but they can be accurate enough to get "in the ballpark", and sometimes it's important to make your very first shots count, before you receive a hail of return fire. Magnified sights can be difficult to use in an intense firefight simply because the process takes too long, but there are situations where they can be used, both as a spotting device, and to aim the gun.  Non-magnified red dot sights can be especially useful since they are quick to use. Even the open sights on older guns are useful for trying to put your first shot on target.  Whether sights are useful or not depends entirely on your situation and your style of play.
 

High Pressure Air is better than Co2
The perception that HPA or High Pressure Air is better in all situations is largely a byproduct of the fact that HPA systems are much more expensive than Co2, and some of the more expensive guns on the market require HPA use only. Co2 does present several problems to be overcome when compared to HPA, however, controlled Co2 (i.e. regulated) can be used just as effectively. Unlike HPA, Co2 is sensitive to temperature changes, which causes pressure fluctuations.  However, for guns operating at pressures lower than those fluctuations , Co2 is probably more effective, since it is stored in a more dense liquid form. In other words, you get more Co2 in a given size tank.
Steve Davidson writes: You neglected to mention that MOST HP is cleaner than most CO2, and, while you did touch on the environmental issues, you tend to minimize their effect;  any player trying to get their gun up to speed in the middle of winter will tell you that environmental factors for all weather play put HP way over the top when comparing it to CO2

There is no such thing as a paintball "sniper"
There is a valid argument that there can be no paintball snipers since all paintball guns shoot the same maximum velocity and you can't have a gun with substantially better range than your opponents. However, in paintball, the term "sniper" is not really about range or the weapon, it's simply a style of playing. While setting up and taking a small amount of shots from a hidden location may not be practical in most small field, limited time games, in larger events like 24 hour scenario games, the tactics can be used very effectively. And it's not simply about aiming the gun and making shots count (the so-called "marksman" label). It's also about using stealth tactics to get yourself into an effective position, and being single minded and determined in your purpose. Many people who play the sniper role wear ghillie suits, continuously crawl, and have great patience in achieving their objective. Some work with teammates to set up ambushes. People who play the sniper role in scenario games are some of the most aggressive players I've seen, and if they want to call themselves "snipers", then I won't argue with them.
Steve Davidson writes:  The negative reaction to this term comes from two places;  the attempt to distance paintball from military association/anti-scenario game hype AND the fact that what paintball "snipers" do is no different from what we all used to do during pump play in the woods;  the 'sniper' skill set was essential to play back then and calling a player who had those skills anything other than a 'player' was just embellishment.   When you talk to players who covet the 'sniper' role, the vast majority are not referring to being patient, using stalking skills and etc., but do have in mind the Hollywood image of someone who gets eliminations from extended range.

Professional paintball players actually exist
As of the writing of this page, I am not aware of anyone who plays paintball as a profession. While many people do make their livings from the paintball industry, they do not actually play the game for their livelihood - not in the sense that Michael Jordan was a professional basketball player, or Richard Petty was a professional race car driver. While the so-called "Pro" teams certainly are the upper echelon of the paintball playing world, even their tournament circuits do not pay enough for them to all make a living just playing paintball, and most of them have "real" jobs they go back to during the week.
 

It's not about the money