That kinda hosed.
The problem was, things were only borked in Ubuntu -- terminal worked fine. So I rage for awhile, make sure I'm running the latest version of VirtualBox, blow away my xorg.conf file repeatedly until I'm sure that's not the problem -- even circumnavigate the globe via the jigsawed Ubuntu to re-install the VirtualBox guest additions, because I totally forgot how to mount cdroms via the command line. >:(
As it turns out, something caught my eye on the settings screen -- the number "9."
"Video memory: 9."
Thinking about it for a moment, I quickly created a new, blank virtual machine to inspect its default settings: identical, except for one area. "Video memory: 8."
Yeah. Guess what started working again once I modified my Ubuntu virtual machine's video memory to 8 megs instead of 9?
It's no surprise my Googling was fraught with much peril and little treasure. I bet practically nobody modifies the video memory setting, much less modifying it to an uneven number. Why does VirtualBox that let you put in uneven values for memory, anyway? Seems like a booby-trap waiting to happen.
I had a backup of the virtual machine from earlier this morning (a literal backup), but damn, I had spent almost 2 hours upgrading Ubuntu to 8.10, and a part of me just didn't want to let it go.
Well, I caught my white whale for this week.