Doncha added, support for off-loading (caching) entire site at once in latest version of wp-super-cache.
I guess same option for page-caching module will be good in w3 total cache.
Also, it we can load entire sites page-cache in APC cache (memory) that will be amazing!
WP-Admin have lots of js/css...
If they can be minified/compressed/hosted on CDN, we may see performance gain.
There was a turbo button in wordpress sometime back for Google gears support, whose codes/functionality may be useful.
Turbo and google gears support is still there, only thing - Google is not updating google gears to make it work with new firefox versions. :-(
Last 2 lines may sound off-topic, but idea is to load js/css needed by wp-admin and specially post-editor as combined, minified and/or from CDN.
Thanks again for great plugin!