I tried commuting using Look pedals this summer, and eventually I was okay at getting in pretty efficiently on starts (I have a 20 mile one way commute, involving mostly MUP but the beginning 2-3 miles and ending 3-4 miles are city streets, where I have to start/stop every 500/1000 feet or so).

One other huge advantage to SPDs for commuting is that the steel cleats don't wear out nearly as quickly as Look cleats. Admittedly, I've learned to protect them better over time, but even being pretty careful, I doubt I would ever get much more than 6 months out of a set of Looks in regular commuting duty, where I've been running the same SPD cleats for over 2 years with no issues. I have a pair of MTB shoes that I use most of the time because they look like sneakers and I can walk without clicking too badly. I also have a pair of road shoes that will accept SPD cleats, but I find them all but impossible to walk in off the bike because they have no traction!