I second the notion that riding in the cold can be comfortable. You just have to dress for it. You're going to sweat even when the temps are in the 20's so the key is to keep the wind from cutting through to the skin and have layers that wick the moisture away.

You're not going to be as fast in colder temps and it's more laboring to ride...... but good gosh, you're outdoors, the air is crisp and after the blood gets going it feels terrific. I haven't found a better way to clear the sinuses either!!

I found some nice toe warmers in the hunting section of Wally world that adhere to the tops of my socks over my toes and they do a fantastic job with keeping the toes warm. The first few minutes can be a little chilly but after that it is very comfortable.