I wear the same pair of pants every time, and rotate through about 7 or 8 T-shirts each workout. On days when I don't do cardio, I can usually wear the T-shirt once more, but on cardio days I am soaked with sweat and smell disgusting!.
Fiancee wears a pair of black yoga pants and a random t-shirt... but she never smells and doesn't usually sweat in the gym (trying to help her up the intensity a bit - but the TV's in front of the treadmills/bikes distract her!)
I do get a kick out of the girls in ultra-tight and ultra-sexy workout clothes
Add in the guys that keep checking out their own biceps in the mirror and it's always good for a chuckle