Definitely takes time to adjust. I was doing half-commutes (multi-modal) a few days a week about a year ago. The second half of last year I rode at least a half-commute every day. In 2012 I haven't done any multi-modal commutes, so I'm riding ~20mi and +1500ft every day which actually doesn't feel bad at all. Although this last week I've been adding miles and elevation (for a stupid Strava challenge) and I think I'm starting to hit The Wall.