Microsoft have advertised for developers to help create a new backend game system that can support up to 300,000 player games...Read the advert here...
“We are building an extremely high performance system to extend console games to the server in new was; creating a completely new set of web services to support dynamic programming information of games and scheduling data.”
The engineer will be responsible for “building a backend capable of hosting a 300,000 player game in real-time with real money on the line (anti-cheating, etc).”