What is Reddit's opinion of Seven Databases in Seven Weeks: A Guide to Modern Databases and the NoSQL Movement?

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thanks, it means "egg thrower" in German^^

In general, I think, go with a relational/SQL database – simply because there’s much more you can do with it. They can handle complex data (with many relations) they allow for great ad-hoc analysis (queries) and they are programmable (stored procedures/functions) – least but not last, the vast amount of tools available.

As you might know there are different kind of NoSql-Databases, Document Stores, Graphs, Key/Value Stores... Each fits its very own purpose. Should you need any of the features they offer and feeling limited by a relational DB, consider switching, or add it to the application where it’s useful. But never forget: There’s always a price to pay. That also goes for MongoDB. You may win benefits, but there are some drawbacks.

To me, NoSql's are not as flexible and universal like relational/SQL databases, hence limited their use cases.

I’ve only worked with MongoDB and Redis myself. They're used at my company as well. Can’t say much about production management, since I never worked as a DBA, I’m from the dev side. However sharding is a nice concept, first encountered it in Teradata.

Some years ago I worked myself through this book. Which was a great start into the NoSql world. Just found out, there's a second edition now. Riak is obviously dead (was used in the mobile game "flappy bird") and replaced with Postgresql.