I said that I would only use it for a toy project. Or at least a project for whose requirements resulted in MongoDB being a good choice. For example a content site where losing some data doesn't matter and whose hot datasets would never expand above the memory available by my budget.

Given the projects I chose to work on, MongoDB would be a bad choice. So I would only use it for a toy project right now. In 3-5 years time I expect that it will be a very good choice, given that they've pretty much won and can hire all of the good engineering talent.

The parallels with MySQL are really astounding; I just hope that they don't end up being sold to Oracle or Microsoft.