This really puzzled me. I noticed à 30% of avahi daemon on Kubuntu 10.10 on a Lenovo T410 (this is the value given by top, not by the task manager of krunner).
This was far too high. Trying to supress plasmoid one by one I managed to narrow down the CPU usage to the system tray. Then I did a few more test and actually everything is just until is open the Network manager in the system tray and log to my wired connection. So it seems that asking kubuntu to use a wired connection make the avahi daemon using 30% of the CPU. Turning it down doesn't make it down afterward.
Do you knwo what could cause this problem? Anyone else realised that?
EDIT: After a few more test I can confirm this is really a problem due to wired connection, it doesn't do that with a wireless connection.
EDIT#2: I checked from home. This is not a problem with every eth0 connection. At home where dhcp works I don't see the boost in CPU usage. It's only from work, where I add to manualy enter the ip adress gateway et al. Also removing the internet cable drop the cpu usage down. Very strange.