When you're not operating at significant scale, you can use a relational database. They're easy and fast to set up, have nice write-safety guarantees, are more flexible than a key-value store, and will scale well beyond anything that mongo has ever achieved. You can even use them as a key-value store! The downside, of course, is that you have to a tiny bit of knowledge about set theory, and that's a deal breaker for most "developers" today.

The whole point of the GP was that Mongo isn't elegant or easy...it's just naive and short-sighted, and the architectural mistakes within it are fundamental and probably unfixable (at least, not without killing the speed advantages they claim). The real reason that people use mongo is that most webapp devs don't have a very good understanding of how computers work, and want everything to look like Javascript, because that's all they really know.