Spice - i know lots of guys that prefer the "short john" aka knee skin body suit. usually sprint breastrokers, and sometimes sprint freestylers as well.
bogus - typically, the longer the race, the less suit is usually worn (tho i know some distance guys that still wear legs). the thought process behind this is most people think that after being submerged in the water for more than 2+ish minutes the suit generally becomes saturated and heavy with water and loses its effectiveness. i personally agree with this, tho there are still plenty of Olympians who will wear legs, etc for the 400MtrFree and upwards. The newer suits, particular the newest Speedo model, are getting better and using less/lighter material, to prevent the suit from being so heavy when it gets wet. if you compare the older models, say Speedo's original "FaskSkin" vs. the new "FSPro", the difference when wet is tremendous. the original is very heavy, while the newer barely feels wet at all.
another factor that comes into play when choosing a suit is body fat. one of the main ideas behind a full body suit is that it restricts all the excess body fat, and even compresses muscle, thus creating less drag. a taller, leaner swimmer would not benefit from a full body nearly as much as a bigger, stockier (not necessarily fatter, but you know what i mean) swimmer. If you look at a masters meet, or talk to any masters swimmer, they will swear by the full body suits, because their bodies have more excess drag than they used to in their younger years, and they are still able to swim times faster than, or very close to the times they swam in their "prime" because the suit helped contain their extra drag.
sorry if i got a little carried away, but that should answer some questions
