The microsoft AJAX toolkit was nice early on. Now developers are finding it is a bit heavy on the javascript and processing. To help solve this issue microsoft is now pushing the Javascript files from a CDN for you to use.
This is great as a server administrator. Users will pull the AJAX (javascript) files from a microsoft server instead of your server.  Savings can be seen in the time serving the file and also the bandwidth.
QUOTE:
By taking advantage of the Microsoft Ajax CDN, you can significantly
improve the performance of your Ajax applications. The contents of the
Microsoft Ajax CDN are cached on servers located around the world. In
addition, the Microsoft Ajax CDN enables browsers to reuse cached
JavaScript files for Web sites that are located in different domains.
