Comment 2 for bug 136962

Okay, in looking this over, I see a few things that you will want to improve upon.

1) If your shipping an update notifier notification that is installed to $unud unconditionally, you need to depend upon update-notifier | adept-notifier. If you don't want to depend on update-notifier, check if that directory exists, and then check if the file exists only if the directory exists.
2) In your postinst you need to define $unud in that postinst.
3) This is a matter of preference, but In your update-notifier warning, I think you should let people know about the config option to turn on and off Xgl.
4) Should Xgl-session really be in everyone's default $PATH? Since its not intended to be regularly executed by a user (but rather by the session), perhaps it makes more sense to be put in a /usr/share/xserver-xgl or something to that effect? I recall a few apps that did that (at least some time back) being vino's server, and gnome-settings-daemon.