But I realize this kind of anti-phishing checking is beyond most users, and "Just don't enter your facebook password anywhere but when you are logging into facebook" probably IS a good heuristic for them.
I also don't know if some facebook oauth login paths use some kind of fancy ajax window-in-a-window so you _don't_ actually see facebook.com in your address bar -- which would make it pretty impossible for users to know if they're being phished or not.