According to this article, all you need is cloud computing and a NoSQL database to scale to 36 million users. Really great journalism.
Would be interesting to know if OMGPOP was planning for or had the expertise to manage this level of scalability - or if they were broadsided by an unexpected hit and called in Couchbase after they started blowing up?
Article doesn't say much other than "they reconfigured some stuff and added some servers" which isn't really a "How".