There is a good blog post by Robert Fox on entitled “Evolution of Hybrid NoSQL to Tackle Big Data” that is worth a read.  Robert talks about the reason for the rise and evolution of NoSQL technologies.  He goes on to explain a little about the CAP theorem and the need to relax the requirements of ACID on a scalable database.  He also mentions Google’s F1 and comes around to how this could challenge the CAP theorem.  A nice summary of the theories behind NoSQL.

Robert also listed a lot of issues that enterprises are facing around implementing NoSQL:
1. Tools are immature
2. Immature solution
3. Lack of domain expertise
4. Lack of support
5. Lack of SQL grammar
The so-called NoSQL vendors are definitely working to address these issues and things today are much better than they were 2 years ago.  However, lots of work does still need to be done.

Roberts’s post is definitely worth a read.