Hi, i've a really serious experience on mongodb, i've totally build some apps in production with clustering, sharding, replicaset, tools to backup for system maintenance with millions records in. I really know very well mongoid, which is the best driver for mongo in ror projects, to build regular queris or aggregation and other complex setup depend on your needs.
Best regards
Olivier D.
PS : could you explain me what did you expect for the project milestone. Thanks.