fishb0y:It seems like someone says this every time, and again my answer is...
If you are doing a long surface swim, go on your back, if the water is too rough on your way out, don't go. If it is too rough on your way back in, use your regulator. I never saw a wave drop into a reg. That is what that extra gas in your tank is for.
I know of a couple instances where people have nearly killed themselves relying on their regulator on the surface. It usually requires a diver who's breaking lots of protocol... coming up with two hundred PSI, not inflating their BCDs, diving with the currents at the start of the dive, etc.
A tank can only hold a finite amount of air. Conditions can change during a dive. Having at least a stow away snorkel can make a big difference on some occasions.