Generally, the pros and cons list should be isolated down to a given implementation. While you can vaguely state that NoSQL data stores are fast, and that horizontal scaling is generally easier on NoSQL, that isn't always the case, and doesn't apply to anywhere close to every situation.
MongoDB offers some REALLY cool features that enhance development speed. Inserting into a table that doesn't exist? It creates the table on the fly. Querying from a table that doesn't exist just returns an empty result set (instead of an error, or exception).
If I had to speak in specifics though, I think it's pretty easy to say that NoSQL stores allow for querying very large datasets faster than you could on a relational store on similar hardware.