Esse problema foi resolvido desde que comecei a usar o 11.10. (11.04 no i7 com 4 core / 8 thread causa este problema)
Consegui reproduzir isso por:
1) having a system which has i7 processor and more core/threads like 2600 model
2) having 8GB RAM etc higher profile
3) 11.04 install and apply reboot
never properly rebooted back. Same system after putting 11.10, it just works perfectly.