Yep, there are violating records

db/migrate/20110330230206_pm_foreign_keys.rb

 class PmForeignKeys < ActiveRecord::Migration
+  def self.delete_disconnected_cvs
+    execute <<SQL
+    DELETE conversation_visibilities FROM conversation_visibilities
+      LEFT OUTER JOIN conversations ON conversation_visibilities.conversation_id = conversations.id
+      LEFT OUTER JOIN people ON conversation_visibilities.person_id = people.id
+    WHERE people.id IS NULL OR conversations.id IS NULL
+SQL
+  end
+  def self.delete_disconnected_messages
+    execute <<SQL
+    DELETE messages FROM messages
+      LEFT OUTER JOIN conversations ON messages.conversation_id = conversations.id
+      LEFT OUTER JOIN people ON messages.author_id = people.id
+    WHERE people.id IS NULL OR conversations.id IS NULL
+SQL
+  end
+  def self.delete_disconnected_conversations
+    execute <<SQL
+    DELETE conversations FROM conversations
+      LEFT OUTER JOIN people ON conversations.author_id = people.id
+    WHERE people.id IS NULL
+SQL
+  end
   def self.up
+    delete_disconnected_conversations
+    delete_disconnected_messages
+    delete_disconnected_cvs
+
     add_foreign_key :conversation_visibilities, :conversations, :dependent => :delete
     add_foreign_key :conversation_visibilities, :people, :dependent => :delete