problem with using a mtb for commuting is you don't have any high gears for speed.
IMHO i would throw some inverted tread street tires or slicks on it and see how much you really get into commuting.
If you find you're commuting more look for a commuter specific bike or get a lower end road or like dave cyclo.
See you on the trail
Couple o' FJ40's, BJ70, PZJ77, UZJ100, TDI