The stack doesn't seem to give an obvious reason for the hang. But I notice in the screenshot that it's mid-animation. And since you're using the nvidia driver, that looks a lot like a known problem (hang) nvidia has with compiz mipmapping. Though as far as I know, the animation plugin does not use mipmapping. So it's not a very solid theory yet.
Have you changed any compiz settings at all in CCSM? Could you please try disabling the animation plugin in ccsm? You get it from package "compizconfig-settings-manager".
Ruben,
The stack doesn't seem to give an obvious reason for the hang. But I notice in the screenshot that it's mid-animation. And since you're using the nvidia driver, that looks a lot like a known problem (hang) nvidia has with compiz mipmapping. Though as far as I know, the animation plugin does not use mipmapping. So it's not a very solid theory yet.
Have you changed any compiz settings at all in CCSM? Could you please try disabling the animation plugin in ccsm? You get it from package "compizconfig- settings- manager" .