10Gen recently published a useful tool developed at one of this year's hackathons between the Drivers and Innovation team. MongoQP is described below:
The heart of mongoqp (Mongo Query Profiler) is a bit of map/reduce JS that aggregates those queries by their BSON skeleton (i.e. keys preserved, but values removed). With queries reduced to their bare structure, any of their statistics can be aggregated, such as average query time, index scans, counts, etc.
You can read further details and check this tool out on Github by reading the original post, available here.