Being the perpetual malcontent, I was trying out themes tonight and at one point I started having trouble with widgets. I noticed in the plugin directory that the widget plugin was listed as "deactivated." I tried reactivating it and got a "plugin cannot be reactivated due to a fatal error" message.
Well, after some monkeying around, I discovered that the widget plugin was still activated and working just fine -- but I can't get it to show up as activated in the plugin list. I've tried changing back to my original theme (which I had to do anyway), I've tried the "deactivate all plugins" button, and what have you, but I can't get the widgets plugin to show as activated in the list.