Some resources on using PostgreSQL with Ruby On Rails
hstore_accessor gem. It provides discrete fields to directly access values in hstore columns to ActiveRecord.
A blog post on using an hstore column for storing hashes with arbitrary keys. His approach is different from the one used in hstore_accessor gem. Aly explains how to store hashes that may have different keys for each record, while hstore_accessor gem implies that hashed in all the records have the same keys.
Next, a very practical article on using Postgres array columns in Rails 4 by Plataformatec. They explain how to use an array column for storing tags.
Finally, a post by Thoughtbot on why PostgreSQL may sometimes not use indexes in SELECT queries.