You can commute on any type of bike. Road bikes are fine. Really depends on your commute and what you carry. I wouldn't ride my Ti bike or a carbon bike on my commute. Not because it wouldn't handle it, but because it doesn't have rack eyelets or fender eyelets. For me this is important because I have to carry stuff and fenders are nice when it's raining on your ride home. I would suggest that if you already have a road bike that can't do these things, to go find a used touring or even a cyclocross bike such as the Surly Crosscheck. These make perfect commuting bikes. Even an old steel mountain bike can be easily converted to a commuter. Go visit the commuting forum. They are very helpful.