Although I don't wear knee warmers, I have a few friends who swear by them.
According to my buddies, the cycling knee warmers keep your joints warm, which helps them to move more efficiently and keeps them from getting injured when you start biking and haven't warmed up yet.
They also say that it provides really good knee support, which is a big deal when you go trail riding and stuff like that.
So I have to say that I'm pretty torn on the whole knee warmers thing. While on the one hand I mercilessly tease my buddies for wearing bright white knee warmers, I can see their point about keeping your joints warm and functioning.
Where do you guys come down on the subject?