Like someone said upthread, it's not the cold but the conditions - I've ridden in 1 and 2 degrees F numerous times. But then again I'm a commuter first and foremost - so any time I need to get to work or somewhere else, I'll usually ride because it's easier.

Riding for fun - I'm not sure we do a huge amount of this in anything below 25 or so, although there was one weekend where we spent a lot of time riding around in the snow! Really, I guess we're such winter sports fans that if it's that cold, we're probably out somewhere skating or xc-skiing!

I'm lucky in that my extremities tend to stay quite warm, and I don't need too much on them. The downside is that I did permanent (or at least long-term) damage to my quads a few years ago, skating in subzero (F) conditions with a wind, and not enough on my legs. So, I have wimpy quads and they need to be kept WARM once it's below 40 or 50! It's a little embarrassing, but they literally just.stop.working!