Preling but not gdm

Gentoo, while it is rare for a stable or even unstable update to completely hose a system, a couple of years ago they pushed through an upgrade to expat which bumped the .so version number, which in turn hosed everything depending on expat. On top of this, the usual tool for fixing missing libraries (revdep-rebuild) had some nasty weaknesses that made fixing one's system decidedly non-trivial. I personally had no idea what expat was or how much of a system depended on it (nearly everything that ran in X to start). There are still people running into this as the support thread for the issue in the Gentoo forums shows.