On the way home in the morning, I kept feeling like something was wrong, like something is slowing me down, but couldn't quite figure it. Was in such a bad mood as a result too. Tonight, on the way out, I'm all dressed and about to be out the door when I notice that the rear tire is completely flat. I can't believe I didn't notice that this was the problem in the morning.
Still, this was my first flat on this bike (about 800 miles in total, 4th week of commuting) and my first time changing a tube since I was 8 and I was glad that I was prepared. As mentioned in quite a few commuting articles, I was glad that I could do my first in a warm, well lit room instead of freezing my ass off in the dark.
Lessons learned: Keep a pair of latex gloves in the seatbag; that grease and dirt does not come off easily.
The rest of the way in was quite pleasant, with an added feel-good sensation stemming from the fact that I didn't say "Screw it" and cage it. Dressed lighter then usual for the 45 degree weather which turned out well. That entirely-too-expensive Descente wind-layer base I got a couple weeks back is really turning out great for this weather with just a single layer on top.