I've been running ubuntu 12.04 for the last month without any problem, just yesterday a problem with the video performance came up.
I'm using compiz (always used it) but now, everything is slower and heavy.. like playing a game at 15 FPS.
I didn't install any updates recently.. so I'm using same old drivers as two days ago when everything was working great.
Dell Studio 1558 - Intel HD - 4GB RAM - 250 GB HD - Ubuntu as main and unique OS with a secondary screen connected to the laptop to extend the desktop.