Shorty wetsuit ok for triathlons?

I've never owned a wetsuit, but I recently returned from a lake vacation where I borrowed a friend's shorty wetsuit (I THINK it was Body Glove, but I can't remember) for water skiing, and ended up loving it so much, I swam across the lake in it one morning.

Now I'm totally sold on the idea of a wetsuit--I did my HIM last year in 64 degree water, and I dealt with it, though I was one of only two people who showed up without one--but wasn't sure what the proper style is for triathlons. I know it also depends on where you're doing your triathlons, so for my purposes: I'm doing mostly the standard northeast-area season triathlons--late spring to early fall in NJ, NY, PA, CT, DE, etc.--and I'm planning on doing IMLP 2010.

Is a shorty wetsuit acceptable for swimming or is it only meant for water sports like waterskiing or surfing and whatnot? Should I specifically look for a sleeveless one (the one I used had short sleeves and I didn't have any problems moving around in it, though to be fair, it was only a 1,200 yd OWS, so perhaps a poor indicator for IM?). Should I just go for the full suit, or is that overkill?

Thanks for the advice!