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....

[barry.wordpress.com...]
[wordpress.tv...]

You might also check out Mark Jaquith's talk
[2011.sf.wordcamp.org...]

That might lead you to some other resources