I updated Ubuntu 12.04 yesterday (09/01/2013).
After the update (updated the kernel, and several other things that I noticed), it's requested a system reboot.
Rebooted: Unity 3D is loaded (only the vertical bar), the "Unity background is purple" and nothing else is loaded icons, top bar, etc. (CTRL+ALT+F1 doesn't work, it's completed freeze).
Only works the Unity 2D or XFCE.
➜ ~ sudo glxspheres Polygons in scene: 62464 Visual ID of window: 0xa6 Context is Direct OpenGL Renderer: Mesa DRI Intel(R) Sandybridge Mobile 60.171477 frames/sec - 67.151368 Mpixels/sec 60.013886 frames/sec - 66.975496 Mpixels/sec 59.871287 frames/sec - 66.816357 Mpixels/sec ➜ ~ sudo optirun glxspheres Polygons in scene: 62464 Visual ID of window: 0x21 Context is Direct OpenGL Renderer: GeForce GT 540M/PCIe/SSE2 94.500831 frames/sec - 105.462928 Mpixels/sec 96.664706 frames/sec - 107.877811 Mpixels/sec 96.986230 frames/sec - 108.236633 Mpixels/sec 107.303790 frames/sec - 119.751029 Mpixels/sec ➜ ~
OS: Ubuntu 12.04 x64
Notebook: DELL XPS L502X
Graphic Card: Nvidia GT540m 2gb
Sorry about my english.