So apparently hitting that "install update" button was a bad plan. Doing so appeared to run the appropriate installation routine, but on the final reboot it gets stuck:
Powers on, M appears, no problem.
"Droid" gets drawn on the screen, no problem.
Red eye appears, no problem.
Then the screen goes blank for about 5 seconds, and "Droid" gets drawn again.
This cycle repeated endlessly for about 2 hours before I gave up and pulled the battery.
I've tried hard resetting via battery pulling several times. I've tried pulling the SD card and booting it. Everything has resulted in the same endless cycle.
I do so love updates that brick my phone! Especially since it's my only phone at home... Any help would be greatly appreciated!!