I'm using a USB keyboard but it wasn't like this right after I installed 12.04x64
One detail though: right after I installed the AMD Radeon drivers both the GRUB screen and Ubuntu's boot sequence looked different, specially the Ubuntu screen which now seems lowdef and stretched.
Update: uninstalling the drivers seemed to have fixed this, but now I don't know how it will affect the performance of my system.
Update 2: the problem is back, and now flash video stops after a few seconds (don't know if related but since it started at the same time...)