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I for one like the concept of storing JSON-like data structures and using javascript-based indices on top of that, like you can do with CouchDB or MongoDB. For the greater part, having something where you can store big amorphous blobs is much less useful than something where you can (a) work on a standard format (usable at least from Java and Python) and (b) use some indices to speed up access via selected attributes.

For a project of mine, I've setup something where the frontend (i.e. javascript) munches on some data structures, which are then passed on to the backend (some Python code for business logic and authentification) which sticks them into the database more or less directly. Works really well, although MongoDB still has this "embrace of the exotic stranger" feeling (i.e., you wonder when exactly your database will stop to like you and just crash), whereas CouchDB is just too slow for my purposes.