Most of these new NOSQL systems scale without additional effort.
This simply is not true. Many of them only “scale” using consistent hashing in the client (e.g. redis, tokyo?), which means that you’re still responsible for figuring out how to rebalance shards when the time comes. That’s extra effort.
Many of the popular NoSQL dbs don’t partition at all. Couch certainly doesn’t. Mongo’s “auto-sharding” is still in alpha, and I’m not aware of any major deployments of it.
Cassandra can partition data automatically, but as of the current released version, you can’t remove capacity.
NoSQL != automatic scalability.