I was also mystified by presta valves at first as all pumps I had used before worked only with shraeder (this might not be the case, perhaps it worked with presta but since I never used presta I didn't take note). Now I really prefer the presta valves, as robartsd points out, much easier to deflate when changing tires, they are mechanically simpler, and you can partially inflate them by blowing into them (I do this with new tubes before putting them in so that it is easier for the CO2 cartridge to work).
I do keep a converter in my toolkit that I carry on my bike, you never know when you'll be out of CO2 and the only pump available is a shraeder, as that style of valve is what is used on cars, also the pump I keep at work is shraeder only.
Pro-tip, don't get the short presta valves, they suck for keeping the pump on them. I have one left currently in commission, once it finally gets a hole I can't patch I'm getting rid of it.