I currently commute on my road bike, which is a pretty aggressive /race style bike. It works to get me from point A to B, but has limitations as a commuter. Primary ones I see are limited options for larger tires, rack, fenders, etc. Riding position is a bit more aggressive, which can be tiring with a backpack, so I really notice any extra weight I need to bring with me on a given day, A rack and pannier would be nice on those days. The skinny tires makes a rougher ride on bad roads, and that plus the brakes makes it a non-ideal commuter in the rain.

I plan to get a new commuter soon, more of a touring or CX style bike - more relaxed geometry, handle larger tires, rack and fender mounts, disc brakes, etc. That will be my primary commuter, though I will still likely commute on my road bike some of the time when I feel like doing a more aggressive ride.