Interesting thread. I don't leave early enough to allow for "buffer" time in the mornings, so I generally ride pretty fast on the way to work. Most of the time I really like the workout and it helps me feel good when I get to work. Unless there is a strong headwind, and then I will feel kind of worn out. But, I'll take a hill over a headwind any day.

There are certain commute sections where I push myself more than others. I usually ride slower through the downtown section of my commute. There are a couple long stretches of road with no lights and a nice bike lane - one is flat and the other is a hill - I generally push myself on these sections unless I'm sore from a prior workout, tired from an overly long day, etc. I ride through a marsh area on my first :15 minutes from home. In the morning, I use that as a warm-up time and on the way home, I make a point to slow down and watch the birds. I love the "magic hour" of sunset time and like to slow down and observe things more at that time of day.

I haven't been doing much riding lately outside of commuting. If I was also doing fast-paced rides on weekends, I would probably be much less inclined to push myself on the commute.