Please read for an updated status on RailsCasts:
Learn more or hide this
GitHub User: envygeeks
For me I had to use the serializer even on a simple model reguardless of it accepting nested attributes. I had a simple table with two fields type and data, where data was hstore and the model had absolutely nothing but validates_presence_of and it would not work until I implemented the serializer, without it, it kept sending it the Raw hash.