diff -Naur calibre-old/src/calibre/gui2/ui.py calibre/src/calibre/gui2/ui.py
--- calibre-old/src/calibre/gui2/ui.py	2012-07-27 09:32:07.000000000 +0300
+++ calibre/src/calibre/gui2/ui.py	2012-08-10 16:14:35.705845033 +0300
@@ -756,7 +756,6 @@
         if write_settings:
             self.write_settings()
         self.check_messages_timer.stop()
-        self.update_checker.terminate()
         self.listener.close()
         self.job_manager.server.close()
         self.job_manager.threaded_server.close()
diff -Naur calibre-old/src/calibre/gui2/update.py calibre/src/calibre/gui2/update.py
--- calibre-old/src/calibre/gui2/update.py	2012-07-27 09:32:07.000000000 +0300
+++ calibre/src/calibre/gui2/update.py	2012-08-10 16:18:17.290074850 +0300
@@ -41,22 +41,6 @@
         while True:
             calibre_update_version = NO_CALIBRE_UPDATE
             plugins_update_found = 0
-            try:
-                version = get_newest_version()
-                if version and version != __version__ and len(version) < 10:
-                    calibre_update_version = version
-            except Exception as e:
-                prints('Failed to check for calibre update:', as_unicode(e))
-            try:
-                update_plugins = get_plugin_updates_available(raise_error=True)
-                if update_plugins is not None:
-                    plugins_update_found = len(update_plugins)
-            except Exception as e:
-                prints('Failed to check for plugin update:', as_unicode(e))
-            if (calibre_update_version != NO_CALIBRE_UPDATE or
-                    plugins_update_found > 0):
-                self.update_found.emit('%s%s%d'%(calibre_update_version,
-                    VSEP, plugins_update_found))
             self.sleep(self.INTERVAL)
 
 class UpdateNotification(QDialog):