AFAIK it's AWS. It used to be hosted by someone else (paid for by PIA in exchange for a permanent ad space) but theymos semi-recently switched (due to concerns related to security and legal ownership, he mentioned it in a post somewhere I think). In terms of hidden identity, I don't think it's really possible to stay anonymous when dealing with a company as large and invasive as Amazon.
At a time the forum was hosted by NForce and still is I suppose, then there is PrivateInternetAccess that had something to do with the hosting if I am not wrong (hosting the server or sponsoring ut, something about)
You've ruined it for me. I always had the idea that the server(s) are located in theymos' living room.
Every morning he comes down and pats his authentication server, the webserver has a coffee machine on it that pours him his morning caffine dose and he gets to work on his workstation (a series of computers that monitor each of ther servers and one big 52" monitor with a desktop computer that he uses to post on the forum with)
.
If that were the case, the coffee would've probably turned into molten lava with the number of DDoS attacks the forum has been hit over the past few years.