You may have done everything you can to optimize the JavaScript resources that you host on your server, but if you find yourself using a Google hosted JavaScript library, Page Speed might be complaining that the max-age of the script isn't quite long enough.
Well, what can you do? It's hosted by a third party. Actually, Google had this in mind when they designed their library hosting service.
If you are accessing a a major or minor release, Google will actually update all "minor-minor" releases automatically.
For instance, if you call
http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/themes/smoothness/jquery-ui.css
Google will return the most current release within the 1.8 minor release, 1.8.16 for example. While this is awesome, it doesn't allow us to leverage long-term HTTP caching, as a new release wouldn't be updated. Hence, Google will only cache it with a max-age of 1 hour.
But, if you are confident and secure with the exact version of a library you are using, simply include the full version number, and you'll find that Google has set the max-age parameter to 1 year! Page speed likes this. i.e.
http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.16/themes/smoothness/jquery-ui.css