I like that bike. Saw one in Minneapolis last weekend for $500.

Single speeds might be a little more efficient. I don't think it is that significant. The real benefit of the singlespeed is robustness, durability, low maintenance, and cost for similar quality. If your commute is not too hilly, you can simplify your ride and save a little time and money on the weekend maintenance. Mostly these advantages come into play in crappy weather and road conditions. Sometimes I think I should be commuting on a beach cruiser. The roads in Minnesota are covered in sand and salt this time of year.