Here is some of what I posted on a similar thread at http://www.wakeworld.com/cgi-bin/Discus4/show.cgi?1/379965
Believe it or not, the Coast Guard does know a thing or two about how to keep bodies afloat. Unless you go under water and take several deep breaths to fully remove all the air out of your lungs and fill them with water, you have not properly determined whether or not your non-CGA vest will float you. This is the biggest misconception in wakeboarding and it's perpetuated by threads like these. JUST BECAUSE A VEST FLOATS YOU WHEN YOU'RE SITTING IN THE WATER, DON'T MAKE THE MISTAKE OF ASSUMING IT WILL ALSO FLOAT YOU WHEN YOU'RE UNCONSCIOUS AND YOUR LUNGS ARE NOT ONLY DEPLETED OF AIR, BUT ARE FILLED WITH WATER
Having your driver "keep a close eye on you" will not always help either. I know of at least one case of a guy that was riding with a non-CGA vest and drowned in only eight feet of water. Both he and the boat crew were professional search and rescue guys, but they still were not able to find him until it was too late.
Obviously, there are people out there that know all the facts and choose to risk riding without a vest anyway. I say more power to them. As long as they are fully informed and know what they are getting into. My problem is when people spread misinformation about non-CGA vests (see above posts) and then others take that bad information and make bad decisions with it. They end up taking risks without being properly informed and that can sometimes end up with bad results.