When I finally launched it again last night--this time directly from its icon in the 'Steam' folder on my Windows 7 star menu--I waited through the pregnant pause filled by the whir of cylinder heads firing and dialogue boxes popping, and then...nothing. Or actually, something inexplicable and puzzling: A new message that read "Updating: 0%."
After several minutes of waiting, the 0% incremented to 1%.
Several hours later, the game was updated...and I was fast asleep in bed.
So much for a productive evening.
It reminded me that Steam has some fairly serious control issues.