Directly from the jQuery Blog:

"As a project, weve never discouraged first time users from using the jQuery Source Code straight from their personal site; it helps to get new users started with development, without having to worry about keeping their code up to date.

Needless to say, the number of users whove directly used the jQuery source directly from the jQuery site has increased dramatically in recent months (with some large-scale sites directly pulling from jQuery.com). This still isnt a huge problem, but its something that the web server hosting jQuery.com shouldnt have to worry about. For that reason, all jQuery source code has been moved to Amazon S3, for example: <a href="http://code.jquery.com/jquery-latest.js">http://code.jquery.com/jquery-latest.js</a>.
The jQuery site has been using the code directly from Amazon S3 for over two weeks now and Ive been very pleased with the results. The number of files requested has dropped dramatically, giving the web server more time to serve the normal jQuery web pages.

Note: All old requests to http://jquery.com/src/& are being redirected to the http://code.jquery.com/& sub-domain (which is managed by Amazon).

A nice thing about this move is that we can soon start providing dedicated hosting for plugins. Once we figure out the logistics of the plugin repository (which is currently under development), well be sure to make that a priority.

Additionally, static jQuery.com files (like stylesheets, images, and JavaScript files) are being hosted directly from Amazon S3 too (static.jquery.com). This is also helping to alleviate any strain on the server that may be present."