Like all technologies MongoDB is a tool and you need to pick the right tool for the right job or in this case the right DB for the right work load. We run 100's of TB of MongoDB with 100's of millions of Mongo Ops. Does it have challenges for sure, does mean you can't scale it no. Here's a talk about scaling MongoDB specifically. http://engineering.objectrocket.com/2014/03/10/scaling-mongo...
Right, but we're disappointed that MongoDB markets itself to fit into NoSQL niche, while it doesn't. If it honestly declared its shortcomings, we'd have nothing against, we'd love it.
For example, it doesn't support crucial for NoSQL "compare-and-set" functionality to avoid transactions/locks. Their best suggestion is to use findAndUpdate() with the full object for "find". And it works (though slow) when you have static schema. But over time you'll want to change your objects, and findAndUpdate() won't find them anymore. Grief. Also, order of fields in nested JSON object matters for findAndUpdate(), so have a happy time debugging why it doesn't find some objects anymore.
