Odi's astoundingly incomplete notesNew entries | Code
Gentoo switches to libxcrypt
Update these packages before others:
emerge -v1 virtual/libcrypt sys-libs/libxcryptOtherwise you can run into dependency issues if there are a lot of other package updates. Also this gets you into a stable state again (as it causes a glibc rebuild) more quickly when you update a system that can't afford longer downtimes.