Busted Knuckles, is it always the rear rim? The front rim I would expect to be the one wearing out as that rim supplies the most braking force, unless you (like my wife) rarely use it. Not an uncommon practice, as many have been told over the years "don't use the front or you'll fly over the handlebars!"

I find it just a little odd that it's the rear - and multiple of them, although I've seen that in a situation with a heavier rider that predominately uses the rear brake. In that case the Kool Stops you may hate, as I've found that while wonderful pads they do wear quicker than some others.