PhD student, 6.5 miles each way. The ride is typically 25-30 minutes door-to-door. My other option is the bus which takes about an hour including the walks to and from the stops.

My summer commuter is a reasonably nice 'cross bike, which gets parked inside the lab. My winter commuter is an X-mart MTB which gets locked outside unless I need to bring it in to thaw cables or something. It's easier to get the bike into the lab than it is to get it into my basement. Last winter saw record snowfall and in the period from Jan.-March I probably took the bus almost as often as I rode. When I listen to the traffic report and it's clear that drivers are incapable of avoiding each other, I don't take chances--I ride the bus.