gotcha for devise gem version 1.0.x, email is case-sensitive, this should fix it

validatable.rb

#  in resource model
#  def self.find_for_authentication(conditions={})
#    case ActiveRecord::Base.connection.adapter_name
#    when 'PostgreSQL'
#      find(:first, :conditions=>['UPPER(email) = ?', conditions[:email].upcase!])
#    else
#      find(:first, :conditions => conditions)
#    end
#  end

module Devise
  module Models

    # Validatable creates all needed validations for a user email and password.
    # It's optional, given you may want to create the validations by yourself.
    # Automatically validate if the email is present, unique and it's format is
    # valid. Also tests presence of password, confirmation and length
    module Validatable
      # All validations used by this module.
      VALIDATIONS = [ :validates_presence_of, :validates_uniqueness_of, :validates_format_of,
                      :validates_confirmation_of, :validates_length_of ].freeze

      def self.included(base)
        assert_validations_api!(base)

        base.class_eval do
          validates_presence_of   :email
          validates_uniqueness_of :email, :scope => authentication_keys[1..-1], :case_sensitive => false, :allow_blank => true
          validates_format_of     :email, :with  => EMAIL_REGEX, :allow_blank => true

          with_options :if => :password_required? do |v|
            v.validates_presence_of     :password
            v.validates_confirmation_of :password
            v.validates_length_of       :password, :within => 6..20, :allow_blank => true
          end
        end
      end

      def self.assert_validations_api!(base) #:nodoc:
        unavailable_validations = VALIDATIONS.select { |v| !base.respond_to?(v) }

        unless unavailable_validations.empty?
          raise "Could not use :validatable module since #{base} does not respond " <<
                "to the following methods: #{unavailable_validations.to_sentence}."
        end
      end
    end
  end
end