Here’s an example of the Facebook Want button.
Currently, publishing want actions is disabled, though the button does render.
The plugin error is
App ... is not allowed to create actions of type product:product.wants for user ...
It’s likely Facebook can then built a universal wishlist that could be queried by other apps through the Graph API.
Currently, querying the me/wants connection on the Graph API shows a blank list, rather than any error.
Update 2: Facebook have since removed the code from the SDK. I’m using an older copy of the code, and the button still works.
Update 3: Facebook have disabled the Want button code. I’ve put up some images of how it looked!