Tichy, give it a spin. The ease of execution (and the sheer speed, even over giant amounts of data) is impressive.
How terse the code is? How easy the code is to read? How likely the code is to be correct? How flexible the data model is to new requirements? How simply you can reason about what the code does?
Reasoning about what the code does is simple once you shift your paradigm to document from relational.
The only advantage of disk-backed hash table is ease of scalability, this is why they're useful for hm.... top 0.005% of web sites, who handle thousands of updates per second.