I was surprised in looking at this thread to see it was from so long ago...
I dunno, Jullianna, I think it goes both ways. I think it's just more acceptable for men to be able to have issues - it's not uncommon to see a guy with a girl who is much more attractive than he, but it's a bit more rare to see it the other way around. Even so, something I look for in someone else is health. I work out frequently and eat healthy and I feel like if I'm going to take care of myself like such, then it shouldn't be unreasonable to look for a man with a similar lifestyle.
That said, I'm also not incredibly thin - or thin even... so I get into this weird mixed place where I feel like how much I do work to be healthy isn't necessarily reflected in "the perfect body" (who are we to try to define perfection anyway?) so how is it okay for me to aspire to find another healthy human?
...I had a couple of friends from camp that were talking a lot over the distance and had come to the conclusion they enjoyed one another and might want to date. The guy, at some point, said something to the affect of "I would still love you if you gained weight." She essentially said that if he gained 100 lbs she would not want to be with him anymore - because she was working hard to stay fit and he'd be letting himself go. I understand her reasoning. I think it's just good to either a) be on the same page or b) not care.