Andrew Montalenti relates parse.ly’s experience with Cassandra. Lots of interesting tidbits, but the money graf is this:
A well-seasoned technologist friend of mine was not at all surprised when I walked him through some of these issues we had with Cassandra. He said, “You honestly expected that adopting a data store at your scale would not require you to learn all of its internals?” He has a point. After all, we didn’t adopt Elasticsearch until we really grokked Lucene.