You're making the arguably extraordinary claim that _someone_ is spinning up Facebook-sized workloads on AWS, multiple times a day. Until you can back that up with a source, you're going to get downvoted.
http://developer.yahoo.com/blogs/hadoop/posts/2008/09/scalin...
Which is from 2008 and which references a cluster twice the size of the facebook one, and mentions several production clusters the same size as the facebook one.
They are (obviously, this being Yahoo!) not on Amazon though.
That's a total of more than 21 PB of configured storage capacity! This is larger than the previously known Yahoo!'s cluster[1] of 14 PB.
Guess they are comparing data volumes. But great for pointing out that they do not have the largest in machine count.
[1] http://developer.yahoo.com/blogs/hadoop/posts/2010/05/scalab...