If you have too many files in /var/lib/pacman, tab-completing a pacman-command will echo "-bash: /usr/bin/find: Argument list too long" at your current cursor position, e.g.:

[root@localhost ~]# pacman -S pac<tab>-bash: /usr/bin/find: Argument list too long

Using the testing, current, extra, unstable and community repos gives enough entries to trigger the bug.

Other (minor) bugs:
- "pacman -<any action><any option> pac<tab>" doesn't work.
- "pacman -A /path/to/som<tab>" will give you "pacman -A /path/to/some " and not "pacman -A /path/to/some/" (notice the trailing space).