I used a road bike for commuting and in May bought a Trek 520 Touring bike. I use the road bike for weekend/tour rides.

I commute on some pretty nasty streets and I'm 220 pounds, and I commute a whole bunch, so my experiences may not apply to you.

I found that I was beating up the road bike pretty substantially and wasn't able to maintain it frequently enough. It was starting to show some serious wear after 900 miles or so of use (which is about 3-4 months or so). As far as flats, I got them regularly -- and this was in the dry season (you tend to have more flats in rain). With my 520, I've had only one flat in 1100 miles and that was basically unavoidable since I ran over what I think was a tank trap.

Having said all this, I see people commuting by road bike regularly. It seems to be no problem with them.