Just released two new Rails plugins for apps using MongoMapper: acts_as_mongo_rateable adds classic rating support plus weighted rates and bayesian averages… and acts_as_mongo_taggable adds standard tagging functionality with some roundup and statistics methods to help build tag clouds and ranked lists. Both have pretty thorough tests, but there are still likely bugs to shake out. Please fork, contribute, and send pull requests if you fix bugs, improve performance, or add new stuff.