Basic hints for MongoDB and MongoMapper newbies.
MongoMapper is very easy to learn because it mainly respects the ActiveRecord API. You will not be lost in a unknown world because you will be able to manipulate your documents as you are currently doing with your AR records. You can persist documents using well-known methods like save, create and update_attributes. You can also select the data you need using finders and conditions. Associations, callbacks and validation are available as well. In fact, the views and the controllers generated by a scaffold can directly be used as they are with MongoMapper.
Before starting your project you’ll probably want to check the list of MongoDB Ruby libraries and watch this presentation giving an overview of MongoDB Ruby libraries. Then in case you decide to dig deeper I’d recommend the series of screencasts introduction MongoDB and MongoMapper.