Genuine question: What are these use cases that MongoDB solves better? I'm a fan of several other non-relational databases, but I haven't really encountered any use-cases for MongoDB that make it seem like a good fit.
- Easy to set up (including replication)
- Fast
- Data in "JSON" format (it's BSON internally)
- Javascript (used for map/reduce mainly)
- Good availability of libraries
Theoretically, CouchDB would have been better, but I've heard some bad stories (remember UbuntuOne)?
I don't have much experience with other NOSQL DBs (except for Redis, it's great, but I like to call it a "DB Toolkit" - I'm not dissing it, I love it)