The memcached list is also regularly scaling porn. Today these gems:
"No clue if we’re the largest installation, but Facebook has roughly 200 dedicated memcached servers in its production environment, plus a small number of others for development and so on. A few of those 200 are hot spares. They are all 16GB 4-core AMD64 boxes, just because that’s where the price/performance sweet spot is for us right now (though it looks like 32GB boxes are getting more economical lately, so I suspect we’ll roll out some of those this year.)"
That's 3200 Gigs (!) of cached data on Facebook. At say 20Kb text per page, that's 160 million cached pages. (I know it's not entire pages they cache, but still). Of course those boxes don't have all their memory for memcached, so it'd be less. :)