paged_scope.rb

module ActiveSupport
  module PagedScope
    def self.extended(base)
      base.scope :paginated, lambda { |page,per_page|
        page ||= 0
        per_page ||= 25

        base.limit( per_page.to_i ).offset( per_page.to_i * page.to_i )
      }
    end
  end
end

class User < ActiveRecord::Base
  extend ActiveSupport::PagedScope
end

>> User.paginated(1,25).count
=> 25