What are the server costs of running Twitter?

I'd be curious on the current amount of infrastructure, machines, data centers etc more than cost even.

Cost is interesting but it isn't as telling a number to me as # of servers, services etc is to me. Of course, I'd be curious to know any of it, as operating at that scale is so interesting.

My guess is it is in the 10's of millions per month for infrastructure costs, servers, network etc.