I commute on an inexpensive mountain bike. I replaced the WTB Velociraptor front tire with a much narrower and pavement treaded tire from th local LBS, WalMart. I left the rear tire alone. It's a WTB Velociraptor. Its wider and has big knobs. I hope they protect me from all the glass I have to roll over getting to work. Even the MUP I use has lots of broken glass on it.

I think people have been using mismatched tires since the invention of the pneumatic tire.

One day, I will get a big street tire for the rear and put a Tuffy liner in it. I commute 22 miles a day, five days a week.