[jeffgrant]

I saw an interview with Spitz where he talked about the suits... said that you had to go 6mph or faster for the drag to be effectively reduced. In some of the races where the swimmers don't have to (or can't) go that fast, they don't wear them. That's why in some of the shorter/faster races, you see Phelps wearing it, in some of the other ones, you don't. (He wears a smaller suit instead).

Also, they are VERY constrictive, which is why you see the swimmers (male, anyway) drop the straps right after they get out of the pool.