Massively takes an interesting look at the server model used by EVE Online. It's unusual for a MMOG because it doesn't divide the player load among different servers or "shards." Instead, the same cluster handles the entire EVE universe and all 300,000 subscribers (total; record concurrent load is around 40,000). The EVE Dev Blog recently announced some upgrades to keep things running smoothly and allow for battles involving over 1,000 ships. They call the technology StacklessIO.