I've always done an alternating pattern of commuting and days off the bike. Even so I'm pretty beat on Friday afternoons after going 3 days during the week, 20 miles each way (in the summer; 13+ in winter), with hills. I go fast, so it's not surprising that I'm tired by the end of the week.
I don't think I could do every day with the distance/pace I keep. I'd have to give up one or the other. Living 20 miles from work, however, limits my options. If I backed off a few MPH I'd end up with a 1h30m commute or more. So, for me, it's riding long and fast, with ample time off the bike for recovery. I cross train on the days off (running, swimming, etc.).