Caching can be done correctly, and once, by us… and developers have to do nothing
使用缓存
Gzip works
支持 gzip 压缩（可以节约用户带宽）
We can serve minified versions
可以使用 js lib 的任何版本
The files are hosted by Google which has a distributed CDN at various points around the world, so the files are “close” to the user
让 google 做我们的 CDN 服务器
The servers are fast
google服务器更快
By using the same URLs, if a critical mass of applications use the Google infrastructure, when someone comes to your application the file may already be loaded!
不同站点共享 cache？
A subtle performance (and security) issue revolves around the headers that you send up and down. Since you are using a special domain (NOTE: not google.com!), no cookies or other verbose headers will be sent up, saving precious bytes.
安全？
完整文档：http://code.google.com/apis/ajaxlibs/documentation/#AjaxLibraries
