For me personally, the perfect commute distance is 5.2 miles, because that's precisely my commute, and riding my bike beats driving a car that distance any day. Therefore, my generally answer to the question is the following: The ideal commuting distance is whatever your commute is.

I know that doesn't answer your question, but I actually really like the five mile commute. Doesn't take too much time away from the family (in fact, it isn't much longer than driving), doesn't get me too sweaty for work and I can always ride longer if I wanted to.