Here’s an example of the Facebook Want button.

Currently, publishing want actions is disabled, though the button does render.

<fb:want href="..."></fb:want>

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: Interested in other unreleased Facebook plugins?

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.