The problem has and always will be that MongoDB toes the line between a caching product and a database product, regardless of what 10gen decides to call it. It's extremely frustrating that 10gen can't embrace this fact, and instead perpetuates marketing that causes the product to be perceived as flawed by their target audience. But once you've discovered this, you can use it appropriately (either by overriding the default silent failure to use it as for durable persistence, or only using it for caching or as an eventually consistent store).
