Single speed doesn't work well here except for the college kids just riding around campus. OTOH, we've got a pile in the back of assorted 5-6-7 speed rear wheels and RDs, so SS conversion as part of the overhaul is pretty rare. It still takes the average new commuter a few weeks before they don't have to walk the worst hills, but a completely rebuilt MTBSO on street tires can last them a few years for $150-200 and be a lot smoother than it was when it rolled out of WalMart. Usually, by the time that wears out enough to need another overhaul, they'll either toss it or have the riding bug and understand why something nicer costs $400+...or they figure out how to work on it themselves and watch for one of those $50 Craigslist steals. Then we still get to sell them parts.