I've heard many times that those belts can go well over 100,000 miles as long as they don't get seriously damaged. I've never once had the slightest problem with the belt on any of the H-D's I've owned - wish I could say that about everything else on those bikes!
Last week I was with some guys, all of us on our bikes, and as we were passing one of the worst public housing projects in the city one of the bike busted a belt. This was about 9pm on a hot humid night in front of a place notorious for drugs, shootings, fights, murder, cats and dogs having sex and all around mayhem. It also happens to be on a major road running through the city so its inevitable to ride by it to get to the best biker bar with the bike night that was going on. We sat across from this place an hour waiting for this guys other buddy to come with his truck and trailer. But before he did a drunk came by and started talking with one of the other bikers (9 of us all together) who got the drunk to go bring some beer for him. Then the next thing I know another guy and one of the women who were along come running over to the rest of us saying this drunk had a gun under his shirt and we needed to get the hell out of there. Fortunately the trailer showed up shortly thereafter, we loaded up and scooted the out of there like we were headed someplace with free beer and women.