I have been looking at NoSQL database for a couple of years now. I have tried Tokyo Tyrant/Tokyo Cabinet, CouchDB and now I’m trying MongoDB. So far I am really happy with it. Documents are stored as document like CouchDB but you don t have to learn Erlang and Lua to extend it. MongoDB use Javascript all the way.
There is also a good set of drivers (PHP, Ruby, Python, C++,…).
I have been so happy with it that I have created a Zend Framework Cache Backend. You can find it here.
It support tags, auto-cleaning and so far it seems to work. Right now it requires MongoDB 1.1.1 or above as it requires Map/Reduce for some tags operations.
I have other ideas to use MongoDB in connection with Zend Framework.