Every page, bottom right. And it doesn't scroll with the page. Detected, almost just like my random buddy here, with AdBlock Plus.
Poked around the HTML, which says:
<embed type="application/x-shockwave-flash" src="http://www.orkut.com/talk/datastore2.swf" name="plugin" height="100%" width="100%">
Intriguingly, it doesn't seemed to have caught the interest of the Google-baiters. Yet. A Google search for "datastore2.swf" throws up only that blog above, and the directory listing of some enterprising chap who has all the items from the Orkut front page. And an '0wn3d' graphic. Interesting aside, that was - Orkut h4x0r3d? *shakes head* MSN Live Search gives bupkes. Yahoo! Search gives that blog again, with another Portuguese (?) discussion forum. A few (three) Diggs. Some speculation that this is somehow linked to Google Talk.
No doubt this would trigger another wave of privacy concerns with Google. Shady fellows. Can't say they don't deserve it either, not giving Roofie a job properly and all that..