I'd like to see how this compares performance-wise with MongoDB and other JSON-based document stores, especially with data sets that are at a larger scale. I know Mongo tends to start crumbling if it can't fit an entire index in the available memory (which happens when you have a 4GB data set, unfortunately). Have you done any of those comparisons?

That said, this looks really interesting. Though I can't imagine for the life of me why you'd indent such a wonderful project with tabs. ;)