Or would you rather not know that she works out? I love to go, I go a few times a week. I don't do weights or anything "macho", but I do the elliptical/cross trainer. I love it, it makes me toned, I know I'm doing something healthy, it's fun with music, and afterward I always feel great from the endorphins. The guys who know I go to the gym think it's cool that I take care of myself. On the other hand, going to the gym makes you all sweaty and nasty, which makes me wonder if some would perceive it as a turn-off. I doubt most guys prefer a girl when she's in a sweaty state (unless it's in bed) as opposed to shower-fresh with her hair and clothes looking nice.
If the girl is going to the gym and having a nice, solid workout, then yes. If she's walking on the treadmill at 2.0mph while talking on her cell phone, and wearing clothes made for ogling rather than exercise, then I think she's a moron.
Yes its attractive means she cares about fitness which is good.
I actually prefer a heavy hottie myself. Someone who sits on the couch all day, pounds bon-bons while watching soap operas. I want to come home every night to a big bucket of fried chicken and other artery clogging foods. Exercising is NOT sexy.