The gadget http://de.wikipedia.org/wiki/MediaWiki:Gadget-Persoenliche-Bekanntschaften-GUI (I think there are more like this) cannot be activated since June 15. If you select the checkbox in your [[Special:Preferences]] tab and hit "save", the page will be reloaded with saving this flag. The flag or rather the gadget was activated before the MediaWiki-update (2009-06-15). It was turned of for all users by the update.
This is not a gadget-bug, but should be a MediaWiki problem, because some of the gadgets e.g. [[MediaWiki:Gadget-contribsrange]] still work. But this gadget is not included in the HTML-code, send by the server, anymore.
Version: 1.16.x
Severity: major
URL: http://de.wikipedia.org/wiki/Wikipedia_Diskussion:Persönliche_Bekanntschaften#Gadget_kaputt.3F