SUSE uses 5
LinuxProMagazine refers to 5 as being a GUI
http://www.linux.com/articles/114107Gentoo:
* 0 - Halt
* 1 - Single
* 2 - Multi-user, no network
* 3 - Full multi-user with display manager
* 4 - Full multi-user with display manager (Alias for runlevel 3)
* 5 - Full multi-user with display manager (Alias for runlevel 3)
* 6 - Reboot
Debian:
* 0 - Halt
* 1 - Single
* 2 through to 5 - Full multi-user with console logins and display manager if installed
* 6 - Reboot
Red Hat/Fedora:
* 0 - Halt
* 1 - Single user
* 2 - Not used/User definable
* 3 - Full multi-user, console logins only
* 4 - Not used/User definable
* 5 - Full multi-user, with display manager as well as console logins
* 6 - Reboot
http://www.skullbox.net/init.phpUbuntu now uses upstart which, from my understanding is based off of init but differs
http://en.wikipedia.org/wiki/Upstart