My BF doesn't really work out. He does sometimes, but it's not something regular. But, honestly, it doesn't bother me too much. I wish he would, if for no other reason than to make himself feel better. We're both in IT, and I know - from my experiences managing an HD and as a gamer - how crappy you generally feel spending so many hours in the same position in front of a screen.
But it's his choice. I figure if he wants it bad enough, he'll do it. If ever I start worrying about his health, or if he really starts putting on pounds, I'll feel myself obligated to say something as his BF. But he's a long way from that, I think.
(Oh, and it'd be nice to have someone to go to the gym with me. But, *sigh*, wishful thinking...