Automatically add the users that sign up to your rails app to a mailchimp list. I usually do this async via Resque and not exactly like in this snippet

gibbon.rb

Gibbon.api_key = ENV["MAILCHIMP_API_KEY"]

user.rb

require 'gibbon'

after_create :sync_with_mailchimp

def sync_with_mailchimp
    begin

      list_name = "signed up users"

      cm_user_list = Gibbon.lists({:filters => {:list_name => list_name}})

      cm_user_list_id = cm_user_list["data"].first["id"]

      Gibbon.list_subscribe(
          {
              :id => cm_user_list_id,
              :email_address => self.email,
              :double_optin => false,
              :update_existing => true,
              :merge_vars => {:FNAME => self.get_first_name, :LNAME => self.get_last_name}
          }
      )
    rescue => e
      Rails.logger.error "Error adding new user to mailchimp. Msg: #{e}"
    end
  end