Well, today I decided to just go for it :) It was the perfect opportunity, as circumstances allowed me to get a lift back home. Thus, I only needed to do the commute in, not the commute back. Total distance was a little less than 8 miles (12.5 km) to town, plus another 2.5 miles (4 km) later that afternoon to get to a tutoring session.
It wasn't as hard as I thought it would be. Most of the ride (barring the hills) was actually quite nice. After the first couple of kilometres, it was almost all flat ground or downhill, so it was very pleasant. Perfect weather as well. I expected my ass to be more sore from the seat, but it was totally fine...until it came time to get back on the bike. Then I could feel it! Still, I made it without incident, and I should be able to make the same arrangement a couple of times a week for a bit, until I get used to the commute in. Then I can start to ride both in and back on the same day, and virtually eliminate my dependence on car-based transport.
I'm looking forward to doing it again on Thursday. There's something extremely satisfying about looking at a distance 99% of people would consider impassable without a car, and saying "I can just bike that". Still, I'll have to see how things go long term. I don't foresee any problems, especially since the commute should only get easier and faster as time goes on.
Next milestone: Make the commute in twice a week for a month or so.