We aren't sharing stats like this yet.
One thing you can do is look in Google Analytics for your site or app
to see the browser breakdown. GA calls out IE w/ Chrome Frame
separately from "regular" IE, so that can tell you how many of your
users have the plugin.
In our experience so far, the biggest thing that changes those numbers
for any app is prompting users on legacy versions to upgrade or
install GCF. Orkut, for example, now requires IE 7+ or GCF.
Regards