Don't use rails case_sensitive false, it is very slow.

app/models/person.rb

@@ -20,7 +20,7 @@ class Person < ActiveRecord::Base
   has_one :profile
   delegate :last_name, :to => :profile
 
-  before_save :downcase_diaspora_handle
+  before_validation :downcase_diaspora_handle
   def downcase_diaspora_handle
     diaspora_handle.downcase!
   end
@@ -39,7 +39,7 @@ class Person < ActiveRecord::Base
   before_validation :clean_url
 
   validates_presence_of :url, :profile, :serialized_public_key
-  validates_uniqueness_of :diaspora_handle, :case_sensitive => false
+  validates_uniqueness_of :diaspora_handle
 
   scope :searchable, joins(:profile).where(:profiles => {:searchable => true})
 
@@ -230,7 +230,7 @@ class Person < ActiveRecord::Base
   def remove_all_traces
     Notification.joins(:notification_actors).where(:notification_actors => {:person_id => self.id}).all.each{ |n| n.destroy}
   end
-  
+
   def fix_profile
     Webfinger.new(self.diaspora_handle).fetch
     self.reload

app/models/user.rb

@@ -19,7 +19,7 @@ class User < ActiveRecord::Base
   before_validation :set_current_language, :on => :create
 
   validates_presence_of :username
-  validates_uniqueness_of :username, :case_sensitive => false
+  validates_uniqueness_of :username
   validates_format_of :username, :with => /\A[A-Za-z0-9_]+\z/
   validates_length_of :username, :maximum => 32
   validates_inclusion_of :language, :in => AVAILABLE_LANGUAGE_CODES
@@ -76,12 +76,13 @@ class User < ActiveRecord::Base
     self.language = I18n.locale.to_s if self.language.blank?
   end
 
-  def self.find_for_authentication(conditions={})
+  def self.find_for_database_authentication(conditions={})
+    conditions = conditions.dup
     conditions[:username] = conditions[:username].downcase
     if conditions[:username] =~ /^([\w\.%\+\-]+)@([\w\-]+\.)+([\w]{2,})$/i # email regex
       conditions[:email] = conditions.delete(:username)
     end
-    super(conditions)
+    where(conditions).first
   end
 
   def can_add?(person)

db/migrate/20110512220310_downcase_usernames_again.rb

@@ -0,0 +1,10 @@
+require 'db/migrate/20110421120744_downcase_usernames'
+class DowncaseUsernamesAgain < ActiveRecord::Migration
+  def self.up
+    DowncaseUsernames.up
+  end
+
+  def self.down
+    DowncaseUsernames.down
+  end
+end