This is old news, but I only found out about it today and thought it was a pretty interesting service, maybe others who haven’t found out about it can find it useful as well.
Google hosts the following libraries for you:
* jQuery
* jQuery UI
* Prototype
* script.aculo.us
* MooTools
* Dojo
* SWFObject
* Yahoo! User Interface Library (YUI)
You can use any of these libs from your site through a Google loader.
// Now you can use the latest jQuery normally
</script>
Google will update the libraries and they are released and they commit to hosting these libs indefinitely.