A couple of our use-cases include: good KV access (stored user data etc.) and listing blocks of data that has been pre-sorted on disk at insert time (leaderboard records, chat message history etc.). As well, the clustering technology is particularly useful at scale. We work in the games space with some very large games in production, which allows us to spread the load across multiple database nodes and offers us peace of mind regarding redundancy.
What do you mean by KV access isn't it a relational data store? do you store the value as a blog? json? if so how do you then do queries on that value's values?