Google has a content delivery network (CDN) dedicated to serving the most popular open source JavaScript libraries here. This will give you faster delivery and better caching for your clients. The Google CDN chooses the best server to provide the library from based on the client location.
Along with location based delivery it also gives you the benefit of saving load on your server and delivering more of your local content faster. Most popular browsers limit the amount of connections from a server that can be made for downloading content and by pushing off your JavaScript loading onto Google’s servers you are freeing up connections that can be used for the rest of your application.
Currently Google hosts jQuery, Prototype, script.aculo.us, MooTools, Dojo, SWFObject, YUI, and Ext.