My yearly "lets see if Ubuntu is good enough now" a few days ago: installed the beta, froze when I connected the external monitor. Then the same happened with 11. And with Xubuntu. And I went back to Windows 7.
In all seriousness, if this is happening to you send me a private message and we can look over your specs and dig into what could be causing it.
[1] HP Envy 15 3033, Acer S3, Asus TimelineX, Macbook Pro