As I mentioned in a previous post, in the quest for speed i've been experimenting with Google as a CDN by hosting my large js and image files on google's app engine.
I've then been using monitor.us to execute periodic page load queries and plotting the results. So the test:
1. login.asp - this is a small .asp page that has light js files and a single image.
2. index.html (hosting on app engine). This is a very lightweight html file only (no image, no js, no css, no nothing).
3. index-test.html (same simple html file - only hosted on my hostmysite account).
I can then compare load times for all three to determine the impact on load times.
The top chart shows domestic and international load times for the host my site hosted index-test.
The middle chart shows the load times for index.html as hosted on app engine.
The bottom chart shows the load times for login.asp as hosted on hostmysite.com
My conclusion is that for domestic visitors there is very little impact in load times when using the google cdn, however for international visitors there is a gain to be had in the order of about 100 ms.
My recommendation would be to use the google CDN only if you have significant international traffic and/or have a js/css/image heavy site. If the main driver behind load times is the time for the page to compile you won't get much in the way of gain, if your traffic is primarily domestic, same thing.
Good luck and happy coding.