I used to have a 12.1 mile commute (each way) over rolling farmland which was just about perfect. I rode it every day and averaged about 45 minutes in the summer to about 55 minutes in the winter. On really nice days, I would take an alternate route to stretch the return trip an extra 10 miles. That was ideal.

Last September, we moved into a new house and now the commute is 21.8 miles each way with a few big roads and much bigger hills (we live in the Alps, so there isn't much flat road between here and work). I still ride it, but now that I have the option of taking the train, I often do so part of the way in and ride back home. My round trip commute time is about 2.5 hours when I take the morning train and 3 hours when I ride the whole way. The train doesn't save much time, but it cuts out the most dangerous routes and makes winter commuting more comfortable. It's a big chunk of time, but like CCrew said, it's my time and generally the best part of my day.