Speed hack, set expiration on header of certain files, like images and js.

To check the expiration of downloaded files, in chrome, go to the browser cache and poke around.  i.e.

about:cache or chrome://cache/

then, find your resource, and click on it, and it will show you.

For example:

chrome://view-http-cache/http://www.openskyradio.com/images/forum/903cafe.jpg

will show:

HTTP/1.1 200 OK
Date: Mon, 04 Jun 2012 20:30:44 GMT
Server: Apache
Last-Modified: Sat, 07 Jan 2012 19:37:34 GMT
Accept-Ranges: bytes
Cache-Control: max-age=604800
Expires: Mon, 11 Jun 2012 20:30:44 GMT
Age: 0
ETag: "470455f-320c-4b5f54c0bdfea"
Content-Length: 12812
Content-Type: image/jpeg