I've just successfully installed Ubuntu 14.04 (Linux 3.13.0-30) on my Macbook pro retina (11,1) (this model has only an Intel GPU); following this https://help.ubuntu.com/community/MacBookPro11-1/Saucy
If I plug the external Thunderbolt display after the system is loaded, nothing happens; if I plug it before the boot, it was activated but the startup process requires up to 20 mins.
Also, after 5-10 minutes of usage, the system starts to run very slow 'til it completely stucks.
What I can do about this? Many thanks in advance