What I was most impressed with however was the forward thinking nature of the repository. For example I recently upgraded my jQuery library to version 1.3, by using Google, however version 1.3 had several bugs in its release, so when version 1.3.1 came out, Google took the initiative to upgrade for me. let me show you what I mean.
of course if you can choose which version you want, and if you want it minified or uncompressed via the relevant directories, and if a user goes from 1 website using the same js framework being called from google, to your website the framework will already be loaded, meaning that your page will load even quicker, pretty nifty I think. why not check it out for yourself, and see if you notice the difference