I found this interesting article this morning about the benefits of urban mountain biking and some tips on doing it well. It seems like many are basic and the target audience is the uninitiated, but this article is definitely worth a read.
I think the best point are the benefits of riding a mountain bike while urban commuting instead of a skinny-tired road bike. The article mentioned the benefits of tackling rough streets, curbs, and debris in the road,
But I'd also like to add that riding a mountain bike while on your commute also opens up an amazing number of route possibilities that just aren't open to a road bike. With a mountain bike, you can take short cuts across grassy parks and avoid traffic, ride stair cases, tackle curbs and speed bumps quickly and easily, and basically dominate the entire city instead of being worried about hitting a small dip in the pavement and throwing your skinny wheel out of true.
During my short commute to campus, there's one section where I routinely come flying down a hill, rocketing over speed bumps, straight over a sidewalk into a grassy hill, launch off of a man-hole cover that's right above a steep hill and catch some air, and them come blazing down that slope and merge onto a sidewalk at ~25 mph as I bust on over to the appropriate building. You just can't tackle a short cut like that on a road bike or urban cruiser...
Do you commute by bike? If so, do you ride a MTB or some other rig?