I commute on and old lugged steel road bike. With 700x28s the ride is pretty comfortable while still being fast. Wearing a messenger bag and being in a low position kind of sucks though. I like commuting on my girlfriend's bike which is essentially the same as my Bianchi, but can support a rack and milk crate. The position is more relaxed and I don't have to worry about getting so sweaty because of the bag. I'm probably just as fast on her bike as I am on mine...

Speaking of which I think I'm going to start taking her bike from now on. It's starting to get very hot and humid mid day.