Amazon Universal wishlist browser add on

Was just browsing Amazon for a book that i added to the wish list for later consideration as i'm still on the fence about buying it only to learn Amazon have a new browser based add-on that will enable you to setup a Universal Wish List on any browser page.

Personally i chose not to install it as i dont want Amazon to be able to track every single web page i visit ever BUT i love the idea, i can only imagine how much anonymized analytic information Amazon is going to glean from this tool if it takes off.

What other cool "by product" tools have you seen being used eg in the way that users of Foursquare arent the customer but the restaurants are.

Cheers,
Dean