> Does this also affect sys.byteorder and the struct module ?

Doesn't seem to affect sys.byteorder:

$ /usr/bin/python -c "import sys; print sys.byteorder"
big
$ python2.6 -c "import sys; print sys.byteorder"
big


> I think those would be more important to get right than the UTF-16
> codec, since this only uses the native byte ordering for increased
> performance and compatibility with other OS tools. Since UTF-16 is not
> wide-spread on Mac OS X, it's not so much an issue...

It is an issue for Python extensions that use that API. For example, it
is the cause of recent Komodo builds not starting Mac OS X/PowerPC
(http://bugs.activestate.com/show_bug.cgi?id=79366) because the PyXPCOM
extension and embedded Python 2.6 build was getting UTF-16 data mixed up
when talking with Mozilla APIs.

 it would be on
> Windows.