After spotting this thread over on iS's PP forum,
http://www.istockphoto.com/forum_messages.php?threadid=358464&page=1 I checked my own preferences and found I am opted in to the PP.
As mentioned there, it's odd that this has happened, after they said exclusives cannot have files there - why is there even an option - big waste of bandwidth which they seem to be concerned about.
I have been out of the PP since a short braindrain when it was introduced.
Any other exclusives who want to be 'out' should check their preferences, 'just in case'.