i think since aim is a windows program, they use shellexecute to spawn the link that is displayed in your profile (keyword think, i dont know for a fact they do). but when shellexec is used to open a browser window, no referrer is passed, because usually the referrer is an optional field some browsers can mask or change and it certainly isnt required by an http get request. i think you may have to do the method where they click the link with the screenname as a variable in the query string using %s
