Okay, I haven't seen anyone else ask this question yet, but I may have just overlooked it. I just installed Ubuntu 13.04 on my HP laptop and I'm having some pretty annoying graphical problems. Sometimes, my bar at the top of the screen will just go transparent, my icons in my launch bar flicker and disappear, and if I try to play minecraft, i can't see because of the weird graphical glitches. I wish I could post images, but my rep on here isn't high enough. Any help is appreciated.
Knowing what graphics card you have would be helpful.
Install your recommended graphics driver. To do so, go to 'Software & Updates', then go to the 'additional drivers' tab. Select the proprietary driver from your GPU manufacturer; preferably one that's tested if it's available, if not just install the newest one and reboot your machine.
If you have any further questions, feel free to ask. If you're still having issues, come back and provide some updates on the situation.
Hope this helps! Iechyd Da!