Here is a commuter that already is using a belt drive, you can see that there is no need to break or split the frame to install the belt.

http://www.deltacycle.com/product.php?g=69

My guess is that a belt will outlive a chain 10 to 1, belts made of the same material in the same way last hundreds of thousands of miles under much greater stresses on motorcycles and cars, should last a long time on a low stress bike application.