Mine is 20 miles each way. It is almost entirely on paved bike path and I have showers at work so it is enjoyable and helps me through the day.

However, since it has turned cold and I have had to resort to studded tires, the distance has become a bit of a burden. The increased rolling resistance of the snow, ice and tires has made it seem like I am dragging my car behind me the whole trip. Taking nearly 1 1/2 hours now to make the trip, it is more difficult staying warm and dry for that length of time. Well, I have no trouble staying warm but with the increased effort, staying dry is more of a challenge.

Anyway, I may have to cut way back over the winter or shorten up the commute some by driving part way.