ergophobe - 1:55 am on Nov 22, 2011 (gmt 0)
no one has yet achieved this successfully
I think these guys might have figured out how to do it: [wordpress.com...] ;-)
Barry Abrahamson, of Wordpress.com fame, chief "Systems Wrangler" for Automattic, posts and speaks about scaling, load balancing and all that. For example....
You might also check out Mark Jaquith's talk
That might lead you to some other resources