I have recently upgraded to 13.04 and am using unity. I am experiencing two intermittent problems with the graphics:
1) All or part of the screen is taken up by 'noise', which lasts for about a second, see screenshot:
2) The launcher panel freezes. I can still move the mouse and the keyboard responds to function keys (I can dim the screen), but I cannot select anything. At the moment I recover by ctr-alt-f1, and restarting lightdm.
My computer is a Samsung Chronos 7 laptop, model NP700Z5C, with Intel HD 4000 graphics
The same problems occur with lightdm and gdm. I have attempted to install the intel drivers (as the screenshot hints) but these are not indicated as additional drivers in software & updates so I'm not sure whether they are in use.