Why cobblestones were ever a useful means of creating roads I'll never know. Sure, there is a quaint charm to the clickety-clack sound that wheels make when they go over them. And there can be some rollercoaster, stomach-in-your-chest appeal to the jostle that is riding over them. But, practically speaking, they must have been hugely destructive.
Take a look at this street in the Beacon Hill area:
Nevermind driving over this in an all-terrain SUV - which, despite modern luxuries, has to still have some degree of unpleasantness attached to it. (Off-roading in the city, anyone?) Now imagine going down this hill in a horse-drawn cart. Don't forget that you have wooden wheels and no suspension. This would tear your wheels right off! Essentially, by the time you crossed the base of the hill, you would have a really nice horse-drawn sled.
But it does look pretty, that's for sure. Were I living at the turn of the 20th Century or before, I think I'd take my chances with the wooden wagon, too.