- Have you tried in a new user (non-root) account just to test this doesn't happen ?
- Do you have hidden icons in the SystemTray ?
- Are your ATI drivers updated ?
- Do you have any other unofficial widget on your Desktop/Panels ?
- When the problem starts ? Inmediatly after the session start ? after a couple of minutes? after some action ?
Thanks

Okay .. some answers to your questions:
1. I tried with a new account ... effect does NOT appear (but I didn't do much configuration on the plasma desktop) Switching with all my data to this new account doesn't seem to be a good option beacuse that would cause much time for reconfguration or installation of software
2. Yes, I have hidden icons, but nothing special and nothing that has not been there before, when the effect didn't exist ... (except klamav there is nothing special hidden there.
3. My ATI driverr ist 2.1.8494 Release, that is actually the last one I got from the ati repository for opensuse 11.1
4. there are no "unofficial" widgets on my Desktop/Panels at least nothing that might cause this problem as none of them did before ...
5. difficult to answer because I can't control the cpu-load directly after logging in. BUt it seems that it strats to build at least moments after logging in, latest whenn all the preloaded software (kontact/firefox) is running.

Again: this did not appear before I newly reconfigured my desktop after having bug No. 206957 (see there). As far as I can see I have started the plasma config. from scratch ... or is there something else I have to consider?? (if there is, this should maybe be stated more clearly ...

Thanks for your help, Jay

Hmmm ... no one looking at this bug anymore??

Okay: here are some news: Today I have been updating my sytem to the newest Version of KDE 4.3.1 that was available on the Opensuse servers. Additionally there was a new Version of the ATI-Driver, which is now in version 2.1.8543.
The situation in my user-account however has not changed: still mor than 70 -80% load from plasma and xorg. BUt now there's more:
It is definitely a plasma -bug, because when I monitored the plasma in- and output and paused the process fro a moment. the xorg load immediately dropped to a respectable rate of less than 8% ... and it returned immediately to the 70% when I left the monitoring-window again.
The only process that's shown as depending on plasma is the ksysguardd-process ...

Any ideas by now??

Thanks again for your help, Jay

okay , now I had the time to check in detail what really caused the problem:

It was a setting of the system tray widget. Not the fact, that I had hidden icons sitting there, butobviously a combination with another setting.
I came to that by simply deactivating all widgets while at the same time monitoring the cpu-usage. when I had eliminated the syytem tray, usage returned to normal. Then I started playing with the settings of the system-Tray a little bit.
Result: its not the hidden applications alone, but the combination with deactivating the "application-feedback" setting which causes the problem. Immediately after this combination was set, plasma and xorg cpu-usage roared up to 80 or more % ... only reactivating the setting and unhiding ALL icons returned the system to normal. 

You should either eliminate the "application-feedback" setting or add a "caution"-remark or find another workaround ...

If you have any further questions ... send me a mail ...

Great, thanks for your investigation. I could reproduce the bug here.

Here using:

Qt: 4.5.2 (KDE-Qt git commit 0bd84180cd0a6ae5c5eb18c0d3ed74228434608d
        Date:   Mon Aug 24 13:56:57 2009 +0200)
KDE: 4.3.68 (KDE 4.3.68 (KDE 4.4 >= 20090907))
kdelibs svn rev. 1022896 / kdebase svn rev. 1022896
on ArchLinux i686 - Kernel 2.6.30.5

Steps:

- Go the the System Tray widget Settings
- Unselect "Application notifications" from the "Popup Notices" group
- Unselect one or two categories from the "Icons" group
(I'm not sure if you need a Icon of this categories in order to reproduce the bug)
- Apply the settings
- Unhide the icons

Plasma will start to take 50~55% of CPU, and X will take 25~30%

- Reverting the settings we changed previously will slowdown both processes.

Here I can reproduce disabling "Application status" and "Communications" (the only icon is see properly hidden by this settings is "Korgac" (note that unhiding the systemtray icons will not show Korgac; you need to reenable the Icon category in order to see it again))

Regards

Bug 211318 got a slightly different option combination to reproduce this bug.

From bug 211318  comment 4:

"

This is certainly similar, except that if "Application status" and
"Communications" are unchecked there is no problem. The problem only occurs
with "Hardware Control" and either "System Services" or "Application Status".

Incidentally, I am also running this on a Dell Inspiron laptop (though mine is
a 9400).

"

I confirm this behavior too.
I can reproduce it by disabling "Application status" from the "Icons" group of the System Tray widget Settings. The CPU gets over 80% fror plasma-desktop and over 35% for Xorg.
If every option from the "Icons" group of the System Tray widget Settings are enabled then the CPU drops to under 2% for each processes.

I'm running Kubuntu 4.3.3.

(In reply to comment #7)
> I'm running Kubuntu 4.3.3.

I mean, Kubuntu 9.10 with KDE 4.3.3.

As noted by the reporter of bug 218519, when the bug is reproduced, Plasma prints this message continuously on shell:

"plasma-desktop(17454)/plasma SystemTray::TaskArea::addWidgetForTask: widget
already exists, trying to reposition it"

*** Bug 204070 has been marked as a duplicate of this bug. ***

*** Bug 211318 has been marked as a duplicate of this bug. ***

*** Bug 218519 has been marked as a duplicate of this bug. ***

*** Bug 221555 has been marked as a duplicate of this bug. ***

Seems to work in 4.4rc3

It seems to be fixed for me too, here using:

Qt: 4.6.1 (kde-qt master commit 5ccbae0c2d9254efe67599137afec763d4fec0f6
        Date:   Tue Jan 19 20:42:24 2010 +0100)
KDE Development Platform: 4.4.61 (KDE 4.4.61 (KDE 4.5 >= 20100127))
kdelibs svn rev. 1082077 / kdebase svn rev. 1082077
on ArchLinux i686 - Kernel 2.6.32.3

- Could anyone else confirm this on KDE SC 4.4. ?
Regards

Can confirm it is solved for me in KDE SC 4.4.0 / Qt 4.6.1 / Arch Linux i686 / Kernel 2.6.32.8

Confirmed as FIXED, closing. Thanks

The same bug in KDE 4.4.0, Kubuntu 9.10

@Alexander: do you recognize some pattern about which category, once it beings hidden, triggers this bug ?

Now I have figured it out a little. It is the same bug as it was described here previously. But, I can add, that I've updated KDE from version 4.3.5 and when I'm creating a new account in the system and having hidden some icons, after a while, plasma-desktop begins to eat a lot of CPU.
But than, I've completely removed all plasmoids, including panels and added a new one, than added a new tray, hid icons, and I haven't seen that problem again. But I decided to experiment and created a new account, with panels and tray by default, hid icons and I came up against the same problem. So, it is only for a new accounts that are being created by default.
I would say, that I have never came up against that problem before upgrading to KDE 4.4.0 and I had been using KDE for half a year.

I'm getting similar high CPU usage whenever the Battery Monitor plasmoid is hidden within the system tray. Showing the hidden icons in the system tray (clicking the small triangle) or setting the auto hide setting of the plasmoid to "Auto" or "Always Visible" in the System Tray Settings takes care of the issue. I have tried this with the vanilla KDE settings with the same result.

System Details:
Linux kernel: 2.6.32.8
Qt: 4.6.1
KDE: 4.4.0

Note that the bug related to the BatteryWidget@Systray was reported at bug 226391, and fixed for KDE SC 4.4.1.
@Alexander: I guess that your variation of this bug was the same as bug 226391. 
Regards