I just upgraded my host from the Postgres Debian package release 7.4.2-4 to PG 7.4.2-6. I'm running unstable on this host. The default 'datestyle' in /etc/postgresql/postgresql.conf has changed to "SQL,European". I discovered pretty quickly that this breaks the users page, among other things I think (probably anything that calls lc_time_fmt).
The fix is to change it to
datestyle = 'ISO,US'
This probably should be added to the installation docs if it hasn't already.