The belt drive systems for bicycles is interesting, and if service life of other belt drive mechanisms is any indicator, reliable too. I considered a belt drive on a single speed frame, but decided to wait. The reason and the only concern, other than cost, was belt tension. Every belt drive I've seen had an incredible amount of tension on the belt. I'm thinking this can't be good on the bearings/axles, and increase the rolling resistance of the hub. Time will tell I guess.