Ok, thank you. I got really impressed by the number and speed of answers within this short time. - Getting new hope. I always was impressed by the quality of maemo.org.

More Details concerning the problem:

* Updated over Wifi directly on the Device. Update description did say that existing widgets (like facebook) are updated too. Maybe there was a problem (reboot) during update can't remember.
* no devlevel apps installed at all (and do not plan to do so)
* when device get's unstable, there are no running apps execept for facebook-widget, rss-news-widget (update set to manually), foreca-weather-widget (update set to manually), wifi-switcher and g3-switcher
* when device get's unstable, mobile-phone is on, wlan is off, mobile-data-connections are off. no applications except the above listed widgets are running.
* symtoms: screen-unlock-switch on the right side of the device does not react. switch on top of the device does not react. maybe does react some minues later (like heavy cpu-usage). not visible if device is on or off. sometimes device does respond but every operation is extremely slow (even swiping from one destkop to another or pressing trying to anything. not visible what process is running (is there an application to show that? is there an event or error log?). sometimes shutdown does work, sometimes it acts like it was off and starts up. sometimes the screen gets iluminated but shows black. after reboot system reacts normal. When in use reacts normal. when left in standby after half an our or so gets the more and more unstable until not beeing usable anymore. hight battery drain, no application running. all wireless (except mobile phone) off.
*8GB SD Card installed, contains windows-mobile applications and n900 digital images, ebooks (fbreader)
*Applications: Forgot to mention, fbreader, fmtransmitter and fmbooster (both set to off), also irremote (camera-remote-control)

@Bratag: no devlevel installed, but will try to do (uninstall all and reinstall one by one) so with all my regular apps. This was a well running system before the os-update? Do i have to plan to do this on regular base?

@itsandrew: like stated above, no usage at all, no apps except widgets running. no wlan and no mobile-data-connection.

@kd-alex: yes, this is true. i got new hope with all the reply's. more bad that good things are posted. but reflashing every week or so when using only regular apps, is new for me. Did never hat do to that with my previous devices.

@sjgadsby: completed the description above.