I have written a few plugins that use widgets, and had a few support requests when some widgets disappear, often when upgrading or turning off a plugin. Justin Tadlock as now released a solution: a plugin that resets your widgets to remove them from all your sidebars.
I think it is a great idea, you can check out the widget reset plugin at Justin’s site.
(__)
`
That is indeed handy. There's more than one time when I've switched themes only to find out I can no longer use widgets I placed in a different sidebar that is non-existant in the new theme. Good job Justin.