As others have said, you see a fair amount of them in Singlespeed classes in MTB and CX.
And youíre spot on about commuter bikes, because those are great applications for internal gear hubs.
The shop I worked in from 09-12 was down the street from Gates and we sold Spot. Early iterations of the belts were a pain the ass, we saw a lot of weird shit, but itís been cool to see the tech get dialed in.