i ride my MTB bike on the road daily. swap out the nobbies for a set of holy rollers every m-f. i wouldn't really call it 'commuting', more like playing on my way two and from work.

just pedaling your MTB up the road would be kind of dumb. when i wanna do that, i ride the road bike. trashing through the city jumping off everything i can find, now thats dang near as fun as hitting the trails.