I've discovered a reproducible javascript bug in sp12. My bookmarklet for bugmenot.com, which spawns a popup window, is being blocked every time. My preference is set to block only when not requested.
Code:
javascript:(function(){w=open(('http://www.bugmenot.com/view/'+escape(location)),'w','location=no,status=yes,menubar=no,scrollbars=yes,resizable=yes,width=500,height=400,modal=yes,dependent=yes');setTimeout('w.focus()',1000)})();