I have a year round basic and pleasant commute of 14 miles and from May to September I expand it on a progressive training schedule of up to 32 miles. The comfort level of the commute may be a factor in assessing the distance. In addition, I have the luxury of taking a comuter rail back to within two miles of home. I have a long workday and by about 8:00 PM, the train ride beckons more strongly than the bike ride. Nonetheless, while the return trip of 14 miles is not too burdensome if done earlier, I'm probably more psyched to ride in the morning since I don't have to do the reverse.

People at work who mostly live around my suburban workplace ask me why don't I move closer, but I tell them 14 miles is a perfect cycle commuting distance. (In my head I think, "Why do you think they call it sub-urban living? )

There have been a few threads about commuting length and my impression is the concensus that 20 miles each way is a reasonable limit.