I rarely see any other riders on my commute to work (at 11:30pm) but I do occasionaly see people on my way home. Almost always roadies with bad attitudes that don't seem to like a fat kid on a MTB with 2" wide tires passing them on a 2 mile uphill stretch.
I've got mt bikes and I've got road bikes. I'd rather run uphill on the lighter road bikes and their easier spinning lighter wheels/tires.