Sorry, forgot to post back. I'm not having this issue any more, either because of a batch of updates, or else switching to a single static gdm theme that I know works. I'm not sure where the problem came from, but it seems to be resolved now, at least for me.
-- [apport] gdmgreeter crashed with SIGSEGV https://launchpad.net/bugs/89383 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
