I use the Page Speed Service that’s available in Manage Domains here (click Edit on your Fully Hosted domain). And I didn’t have to modify the CNAME record (it’s the same IP address as my non-www domain entry).
When I view my site, my Activity Window shows several Pagespeed entries. They don’t show up in View Source.
If you have Pagespeed enabled on your domain, check the Activity Window of your browser.
On Safari, it’s Option-Command-A
I don’t know what it is in other browsers.