Earlier today the ASP.NET team launched a new Microsoft Ajax CDN (Content Delivery Network) service that provides caching support for AJAX libraries (including jQuery and ASP.NET AJAX). The service is available for free, does not require any registration, and can be used for both commercial and non-commercial purposes.
Scott Guthrie has some more info on his blog, here is the summary
The Microsoft Ajax CDN enables you to significantly improve the performance of ASP.NET Web Forms and ASP.NET MVC applications that use ASP.NET AJAX or jQuery. The service is available for free, does not require any registration, and can be used for both commercial and non-commercial purposes.
read the rest here: http://weblogs.asp.net/scottgu/archive/2009/09/15/announcing-the-microsoft-ajax-cdn.aspx