I've been commuting for a while, but made my first ride in "real" rain this morning. Surprisingly, it wasn't too bad. My average speed was down, due partly to the rain and then partly to the train that I had to wait for. Without fenders, your back will get that nasty road grime all over it.

I'd suggest a cheap rain jacket. And stay away from ponchos.

Oh, and by the way, congrats on your first commute. It'll be hard to stop, now.