With the update to pacman-3.2.1-2, we have split the mirrorlist into the pacman-mirrorlist package. This will allow us to push more frequent updates to the mirrorlist, instead of only updating it with pacman releases. As part of this update, your current /etc/pacman.d/mirrorlist file will be saved as mirrorlist.pacorig and the default mirrorlist put in its place. Remember to merge these files in order to keep using your mirror(s) of choice.
Pacman update and mirrorlist
2008-12-21 - Allan McRae