I am using MongoDB for Cheméo[1]. It is a chemical component properties search engine. The document store is very nice as I can easily store in one document all the data related to a given component (all the properties, the source of the information, etc.).
I keep PostgreSQL for many things, but the "business related" data are stored in Mongo. This is running pretty well and it makes the agile part of the development easy, as one have nearly no impedance miss match between the code and the storage (the MongoDB drivers return ordered dictionaries and lists and I can access them from Python and PHP easily).
I was definitely faster from "idea to market" with Mongo.
I keep PostgreSQL for many things, but the "business related" data are stored in Mongo. This is running pretty well and it makes the agile part of the development easy, as one have nearly no impedance miss match between the code and the storage (the MongoDB drivers return ordered dictionaries and lists and I can access them from Python and PHP easily).
I was definitely faster from "idea to market" with Mongo.
[1] http://www.chemeo.com