It's not ready for primetime in DBs that require a great deal of relational mapping. Best cases are apps with very compartmentalized documents, a more robust caching server or something that doesn't require a lot of cross model mapping.

We found out the hard way with our app, with which we wanted to do a lot of associating and joining of information. You either get locked into the document, or locked into writing interpretive code, and neither case is fun to work around.