Ability to get the URL of where a purchase/opt-in came from

Any marketer gauges their success on a multitude of factors. One of our customers would like to get the page URL that was visited which caused a purchase to happen. While you can tell which form was filled out, you might not always know which page (that form could be on multiple pages).

Landon mentioned a genius suggestion... a merge field that could pull the current URL into a hidden field on a form, so how bout dem apples?!