By default, != returns the opposite of ==, unless the latter returns
NotImplemented.

(Is this worth backporting to 2.6?  It seems so useful...!)
diff --git a/Misc/NEWS b/Misc/NEWS
index c2699ec..4f647d2 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -28,6 +28,9 @@
 Core and Builtins
 -----------------
 
+- By default, != returns the opposite of ==, unless the latter returns
+  NotImplemented.
+
 - Patch #1680961: sys.exitfunc has been removed and replaced with a private
   C-level API.