I recently switched from a commuter hybrid style bike to a road/tourting bike for my 10 mile commute. The only real advantage to the flat bar commuter bike is that the upright position gave me better visibility and control at busy intersections.

However my commute is very suburban and office parky with long stretches of bike path in between busy streets, so for me the faster road style bike is much better. It saves me 5 - 10 minutes on average and allows me to maintain a faster pace on long flats and hill climbs. The road/touring bike is also more versatile - now that I commute, everbody wants me to join their group charity rides, which I had a hard time doing on the commuter.

If I lived in an urban area, I would think the advantages of the road bike wouldn't be realized and I would have stuck with the hybrid just for the upright position and visibility. I felt tall yet stable on the hybrid. I could see over cars easily, and I felt like I was highly visible to others.