I stopped in to the Spot booth to take a look at how the Belt drive works. I talked with one of the guys about the rumor that belt drives slip. I think that in some cases it might be true, but not this one. Getting a belt to slip is damn near impossible with the Polycarb teeth mated to the belt. Getting the belt on and off is really the only drawback that I see since it will require a gap in the drive side rear triangle.
If you are considering a trouble-free commuter that doesn’t leave you greasy - a single speed belt drive might be the way to go. A belt drive on an internally geared hub?! That would be killer.