Kubuntu Performance Problems

[Tobias Baldauf]

For some days now my Kubuntu has severe performance problems. Especially 
animations play like 1frame/second. And typing e.g. mails like this one 
sometimes lag so that a bunch of text appears like 3 seconds later. It 
seems like a process in the background is using a lot of CPU-Power.

Here's the 'BUT': My System-Monitors do not show that any of all the 
processes running uses a large amount of capacity. Everything in these 
processes seems to work fine. And also, the CPU doesn't get hot because 
of large usage - which it should do if it was under heavy usage.

I'm not sure, but I think it all started with some upgrades via apt-get. 
Maybe the new linux-image (kernel)?! I don't know how to find out what 
it is.

Any hints/ pointers?

TIA!

Tobias