Rob and I have been looking at the various kinds of NoSQL databases and looking at the differences between them. We've distilled this into four main types. Key/Value, Column oriented, Document centric and Graph databases.
As a result of this analysis we have just published a paper universalNoSQL.pdf which shows how Globals can be used to model each of these types of database.
Not only can you get all the characteristics of each of the NoSQL database types, but with Globals you get this in a mature package with comparable performance and some extra goodies, like transaction procession, thrown in for good measure. Read this paper universalNoSQL.pdf to find out more about this.