Sorry for being soooo slooooow, but still I got a problem. After upgrading WP from 2.5 to 3.2.1 I cannot get my widgets running.
On the admin widgets page I see no widgets to use. (I have all plugins deactivated). If I activate some 3rd party plugins that provide widgets, those widgets are available to be installed.
The next point is that upon having no widgets to display the sidebar of my blog shows Search line, Archives and Meta (which I conside ARE widgets). Upon activating the plugins providing widgets, the default ones become missing.
So the question is - how do I regain control over the widgets to be displayed? :)