diff -uNr calibre.old/src/calibre/gui2/ui.py calibre/src/calibre/gui2/ui.py
--- calibre.old/src/calibre/gui2/ui.py	2011-01-11 22:08:00.684511166 +0100
+++ calibre/src/calibre/gui2/ui.py	2011-01-11 22:11:34.522099663 +0100
@@ -590,7 +590,7 @@
         if write_settings:
             self.write_settings()
         self.check_messages_timer.stop()
-        self.update_checker.terminate()
+        # self.update_checker.terminate()
         self.listener.close()
         self.job_manager.server.close()
         while self.spare_servers:
diff -uNr calibre.old/src/calibre/gui2/update.py calibre/src/calibre/gui2/update.py
--- calibre.old/src/calibre/gui2/update.py	2011-01-11 22:08:00.684511166 +0100
+++ calibre/src/calibre/gui2/update.py	2011-01-11 22:11:16.678301138 +0100
@@ -87,12 +87,12 @@
 
 class UpdateMixin(object):
 
-    def __init__(self, opts):
-        if not opts.no_update_check:
-            self.update_checker = CheckForUpdates(self)
-            self.update_checker.update_found.connect(self.update_found,
-                    type=Qt.QueuedConnection)
-            self.update_checker.start()
+    #def __init__(self, opts):
+        #if not opts.no_update_check:
+        #    self.update_checker = CheckForUpdates(self)
+        #    self.update_checker.update_found.connect(self.update_found,
+        #            type=Qt.QueuedConnection)
+        #    self.update_checker.start()
 
     def update_found(self, version):
         os = 'windows' if iswindows else 'osx' if isosx else 'linux'