The article entitled: What the heck are you actually using NoSQL for? does a very good job at presenting the pros and cons of using NoSQL.
Edit: Also read http://blog.fatalmind.com/2011/05/13/choosing-nosql-for-the-right-reason/ blog post too
Re-edit: I found some recent material (published in 2014) on this topic that I consider to be relevant: What’s left of NoSQL?