Plugins - IncludeGoogleJs
Add to favoritesIncludeGoogleJs will over ride javascript_include_tag to use Prototype and Script.aculo.us from Google instead of the local copy, as described at http://ajaxian.com/archives/announcing-ajax libraries-api-speed-up-your-ajax-apps-with-googles-infrastructure
Only works in Rails 2.1 so far, will look in to getting it running on older versions soon.
http://github.com/chriswarren/include_google_js/tree/master
git://github.com/chriswarren/include_google_js.git
Rails' (MIT)
Misc. Enhancements

Great add! Can't wait to see the 2.0.2 version.
Thanks!