Thanks for checking out the bike! The guy I bought it from on CL reconditions them and sells them as a hobby and obviously cares quite a bit about them. I've gotten advice from him several times since purchasing on riding basics, floor pumps, etc.
Downtube shifters were (and continue to be) an interesting experience. Having never owned a road bike before, I just assumed that was the way things were.
I've learned to listen to my bike and trim between the two front gear, so as to not ride the chain against the derailleur. What started as a fun hobby and automobile replacement (someone ran a red light and removed the front 2' of my wife's car) is becoming a minor obsession. I'm at about 15 miles per ride at 16mph average thus far (distance meter on the iPhone).
One quick question: As I'm starting to get into this a bit more seriously, what would you consider to my best next step? I was thinking clipless pedals (Look KeO sprint pedals are relatively cheap on ebay) and a decent pair of shoes off nashbar.