Comment 84 for bug 1062077

So I found out, why those "hangs" occur (or better: how to "heal" them):
till now I've had a script in my "autostart"-section which essentially just disabled the dgpu (the power-gpu).
It seems like X.org or something isn't happy with getting "robbed" a card while it is running.

So my solution/fix is:
Deaktivating the card before X.org is even started, by setting up an Upstart-Job:
$ sudo nano /etc/init/disable-gpu.conf # content at: http://paste.ubuntu.com/6131570/

Now everything (including Audio, which had a "separate" bug) works fine, no hangs at shutdown, no problems at suspend/resume, no problems at VT-switching.