When you switch themes all your layout of widgets gets thrown back into the Inactive widgets area for widgets can have multiple invocations and the Available widgets area for those that can only be invoked once.
This is particularly annoying if you have multiple widgetised areas (asides - once known as sidebars) i.e. 13 widgetised areas as in the Thematic framework and are only switching from one child theme to another or to the parent (framework) theme and you know the new theme can handle the existing widgets layout.
Does anyone know of a plugin that can take a snapshot of you widgets in use and make it easy to restore the widgetised areas to what you had.
Searching the plugins repository with sensible tags or keywords leads to a sort the wheat from the chaff situation, plenty of results, but few if any useful results.