Is there a master list somewhere of books that on wish lists?  I have many books that I have not posted, but I would if someone "wished"it.

I don't know if there is a master list somewhere, but there is a Droid app that lets you scan the ISBN with your phone and then checks to see if anyone is wishing for it. 

On the Home page look for the search tab.  When the drop down box shows, second from the bottom you will "Club Wish LIst"  You can search this data base many ways and see before you post a book if it is on someone elses Wish List.   Hope this helps you out.