I have to say that I am happy with the purchase of my Surly ECR as a commuter. With several trips under my belt, I can say that my commuting time seems to be about the same as on my Hardrock. I think I like the ECR better than my Hardrock both on and off the road.
What I haven't been thrilled about is the 2x8 gear setup I brought to the party. I've been thinking about going to an internal-gear hub and may yet, but couldn't bring myself to do that without at least trying it single speed - having had a recent revelation about the value of a single speed on the trail.
Well, I took the plunge and converted it to SS today. I geared a little tall for off road and probably pretty short for the road at 2/1 on 29+. It has positively transformed the bike for unloaded goofing around but I'm a little nervous about how it will be commuting loaded into a headwind. Guess I'll find out soon enough!