I managed one of the largest MongoDB installations and I can safely say running it at scale is extremely difficult. They've made a few changes, like not hardco

I managed one of the largest MongoDB installations and I can safely say running it at scale is extremely difficult. They've made a few changes, like not hardcoding the maximum number of connections and shards anymore, which helps but overall the big problems like database-level locking are serious problems even a year later. The reasons for choosing it were very simple - the lead developer was familiar with JSON and liked using it for queries, and he liked the "schema-less" nature of document storage. No consideration was given to performance or scaling issues, it was purely a comfort level decision.