No they don't, not club level riders anyway. Or at least we didn't when I used to do XC and road riding. Lycra really is fantastically comfy, it doesn't bunch up hour arse, and it lets the air flow through a lot better, so you don't get hot and sweaty as easily. That said, I did stop wearing it when I was about 14 because I felt that I looked like a retard and I didn't fancy my chances if I fell off.