Wow seriously? The ARS article was the first time I'd ever heard of something on this scale. That's crazy!
Indeed. What most of you guys aren't aware of is that inline images can be used to achieve cookie stuffing, since most you have inline images enabled here.
A scumbag will setup a server (typically on a .info domain for some reason) with a number of fake images on them. Said scumbag will then either use bots or turkers to have the fake images posted in various forums as an inline image so that client browsers attempt to load them.
When a browser attempts to load an image, the server will run some logic to try to figure out if they've nabbed you before, and if not they will redirect the image request to a business's website, using a URL that includes their affiliate ID. The business's website in turn will send back a cookie with the affiliate ID, which your browser dutifully accepts and saves. Of course for the browser this was supposed to be an image request and it didn't get an image back, so you either see an empty image box or more often you see nothing. Alternatively, if you have been nabbed before the fake image will come up blank, or they will actually load an image (usually an emoticon) to make it look legit.
So when you see those nonsense posts from newly registered members, sometimes those posts are coming from cookie stuffers. Unfortunately what most of you are not seeing is the fake inline image they're using to stuff you.