So what I'm hearing is, length matters.

Mine used to be somewhat long, 30 miles RT with a 2mi. long steep hill at the very end of the commute in to work, that I had to climb every morning (legs got kind of gummy by the time Friday rolled around), but on the upside, was treated with a descent down that hill at the end of each day. Nothing clears the head like doing 50mph on two skinny tires within 90 seconds of leaving the office.

Now I'm less than 10 miles RT which from a time constraint perspective is great, but I'm not nearly as fit as I was during the longer commute.