i stopped wearing cotton a long time ago because the combination of sweat and friction causes too much wear and tear. i'd be tossing piles of t-shirts into the trash each year if i still wore cotton. when i commute i typically wear a cheap jersey (20 buck serfas or dakine of late) and stretchy climbing/mtbing shorts. in the winter i wear lycra and layers. for me, bike-specific is also much more comfortable than street clothing on a bike.