I wanted to reinstall a friend's Arch system yesterday. I finished installing the base system, then I did a Syu, but didn't realise pacman was updated to version 3.0.5. I did a pacman -Sy xorg, and after generating a xorg.conf with xorgconfig, it seemed that X refused to start. I asked in #archlinux, and someone suggested that I should check the permissions of /usr/bin/Xorg. The permissions looked like this: -rwxrwxrwx root root. After I set suid on that executable, startx worked properly. Also, startx told me that my user has no permission to access /dev/tty0. Starting X under the root account worked though. I only had this problem since upgrading from pacman 3.0.4 to 3.0.5, so I guess it's a recently introduced bug in pacman. I reinstalled the system, did a pacman -Syu --ignore pacman, and installed the old pacman 3.0.4 with pacman -A. Now everything is working fine.