Ubuntu 12.04 has been really unstable in my desktop and I heard from other people experiences similar result. So be aware of it, 10.04 has another year of support and it was rock solid for me, perhaps a mistake in my part to get really excited and upgraded my installation.
The problem I am facing is constant freezes no mouse no keyboard. I have to reboot 3 or 4 time per session, no fun at all.
I have been an Ubuntu fanboy since 8.04 and now I am considering just to ditch it and find a different distro.
Good luck to you!