True, and one of my reasons for putting centos on the desktop was to educate myself about the differences under the hood. I'm aware of the Upstart/init difference, and apparmor/selinux difference. Any references you have to share would be most welcome.

I seem to find that from an end user/desktop user point of view, CentOS delivers much of what Lucid/Squeeze delivered except no banshee (mono libraries not installed). I therefore point out the existence of RHEL clones whenever Ubuntu folk express concern at the shift from Gnome 2 to Unity or Gnome Shell when upgrading from Lucid.

CentOS 6 uses Upstart.