Used to commute on a hybrid. It got stolen (not on the commute) so I switched to a cyclocross, and enjoyed it so much more that I kept doing it even after the cops got the hybrid back. I got the bike fitted with an Old Man Mountain rack (doesn't need braze-ons) so I can use a pannier and don't need to worry about a courier bag. It didn't flap, but did weigh me down in a way I didn't like.