I'm assuming you are only talking about Google's US homepage? (i.e. not including youtube and other non google.com Google properties)?
See: http://www.alexa.com/siteinfo/google.com
Then click on the 'more' link under the flags. Google keeps trying to redirect me to google.nl but I always set it back to google.com and it looks like I'm not alone in that.
For example .co.uk and .com.hk, for example, have a global reach of 3 and 4 percent respectively (I've made a guess that those are the top two alternate domains).
So already that is a significant boost to the Google stats.
(edit: checked .fr, that is another 3% reach)
(edit2: .de and .in are also in the top 20 and contribute 3.5 and 4 percent in their turn. I make that a [rough] grand total of 57.5% reach.)