I recently re-installed Ubuntu on my laptop (Vostro 1700; 2G RAM, Intel Core 2 Duo), and sometimes, a werid very high CPU load kicks in. It doesn't seem to do anything with the program that actually has the high load, because when I kill it, the load just spreads to other processes.
And with high load, I am talking unusably high. Even typing in a terminal lags. Then, after some minutes, the problems calm down and the system is usable again. There is no harddisk action and no strange processes (as I type this, it was Firefox idling up to 60%, eclipse idling at up to 40%.
It also doesn't seem to be a hardware problem, because when the system is not in this high load state, it runs OK.