Taken from debian.

# Description: Disable update check by default.
Index: calibre/src/calibre/gui2/main.py
===================================================================
--- calibre.orig/src/calibre/gui2/main.py	2014-02-02 10:41:28.470954623 +0100
+++ calibre/src/calibre/gui2/main.py	2014-02-02 10:41:56.546954247 +0100
@@ -37,8 +37,8 @@
                       help=_('Start minimized to system tray.'))
     parser.add_option('-v', '--verbose', default=0, action='count',
                       help=_('Ignored, do not use. Present only for legacy reasons'))
-    parser.add_option('--no-update-check', default=False, action='store_true',
-            help=_('Do not check for updates'))
+    parser.add_option('--update-check', dest='no_update_check', default=True, action='store_false',
+            help=_('Check for updates'))
     parser.add_option('--ignore-plugins', default=False, action='store_true',
             help=_('Ignore custom plugins, useful if you installed a plugin'
                 ' that is preventing calibre from starting'))