I've noticed a trend across about 20+ candidates, all of whom are smart people: people are using Mongo without actually understanding what the hell it's trying to solve by getting away from the RDBMS paradigm.
I'm not sure if this is because 10gen markets it as a general purpose tool, but I have yet to talk with a candidate who can actually describe why they were using the DB vs. a SQL database. I'm all for learning new things, but I can't help but wonder if the string of negative MongoDB posts is coming from people who pick it b/c it's new, then realise pretty far in that this is nothing like a normal DB, and "having no schema" isn't really a reason to go with a tool as foundational as a data store.
I think Mongo is great for really specific problems that its designed to solve. It's probably pretty bad for a general purpose tool, but I'd be surprised if anyone serious actually considers it one.
My observation has been that a substantial number of people pick NoSQL stores because they don't really understand RDBMSs, and can't be bothered to learn.
I don't mean this as a dig at NoSQL in general - there's perfectly valid reasons to want some NoSQL features - but the hype train does attract a lot of people who just want the new hotness.
I have talked to more than one 10gen marketing bro who insisted that MongoDB is appropriate for any and all use cases, transient to archival. It's pretty disingenuous if you ask me.
We did not have this experience when I worked at a large datamining company. It was a nightmare.
Mongo markets ease of sharding as an advantage, and if that is not the case at times, it limits the attractiveness of losing RDBMS features.
It is just a setting you know that right ?