I think Robert Graham is behind the curve a bit. Two years ago we were already at 2M connections per box (see http://blog.whatsapp.com/index.php/2012/01/1-million-is-so-2011/) and by Moore's Law alone it should now already be at around 5M. Note that at the architectural level, there is a lot of similarity between nginx and erlang. Arguably, some nosql database systems share that architectural thinking as well.