sys.__stdout__ is quite often abused (two independent sightings on 
c.l.py yesterday): people use it to restore stdout instead of saving 
the previous stdout.

The real intended use for __stdout__ isn't all that clear (I keep 
wondering myself why it's there in the first place; its use case 
must be quite obscure), but more importantly I think the sys docs 
should contain a warning that __stdout__ is *not* suitable to 
restore sys.stdout after redirection.

I'd produce a patch if I knew how to better describe what 
sys.__stdout__ was *for*.

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In IDLE it's useful for debugging:
print>>sys.__stderr__, "!!!BOO!!!"
will print a message to the console no matter what the
redirection status is.  So that's a use in addition to the
two given in the sys module docs.  Agreed that its bad
practice to use them to restore redirection, but that IMO
belongs in a tutorial, not the reference docs....

Current docs seem to explain what __stdout__ is for:
"""
__stdin__ / __stdout__ / __stderr__

These objects contain the original values of stdin, stderr and stdout at
the start of the program. They are used during finalization, and could
be useful to restore the actual files to known working file objects in
case they have been overwritten with a broken object.
"""

Should a note of warning be added? Something like:

Explicitly saving the original IO streams and restoring them after
redirection is safer and the recommended idiom.

Amended documentation in r70867.