I just read an article that gives a lot of good reasons to have jQuery scripts hosted at Google. The article even provides test case with graphical charts. Here is the link:
http://blog.httpwatch.com/2008/07/08/test-drive-of-the-google-hosted-ajax-libraries/
Here are some of the reasons why to use jQuery scripts hosted at Google:
•The libraries are hosted on Google’s high speed global network providing fast access from most locations world wide
•HTTP compression minimizes the size of the download
•Minimized versions each library are available to further reduce download size
•The library that your site uses may already be in the user’s browser cache if the user has visited another site that uses the Google hosted libraries
•You can specify which version of a library should be used with a hard coded URL or allow for automatic version upgrades using the google.load() function
•Downloading from a different hostname (i.e. ajax.googleapis.com) frees up an HTTP connection in the browser that can be used to download other resources from your site
•Google picks up the bandwidth bill for the hosted Javascript libraries