UPDATE: As of 16/3/2012, Identify this game questions are now prohibited on the site.
Take Mike. Mike joined as an unregistered user February 22nd at 19:25:24 Zulu as he posted this question tagged identify-this-question. He last visited on the same day at 23:11:05 Zulu (ranking him above a real lot of unregistered users who leave one post and never look back again).
For normal questions, this isn't really a problem. For ITGs, it is, because he is the only user who can actually say "yes, this is it." An abandoned ITG is just a game-rec in disguise. That's not very good.
However, I should note unregistered users only are tracked via cookies, for lack of anything better; that's the "price" to pay for allowing anonymous users to post.
If When the user clears his cookies, he gets effectively locked out from his account (that's fixable if he requests a merge). This makes, however, the last seen value less useful. For all we know, he could've cleared his cookies on the 23rd and checked the question every day since. It's however quite unlikely, and human exception handlers can probably take care of this situation.
So: when can we declare an ITG question abandoned? What should we do about them?
Keep in mind that the condition must be actually enforceable. If your abandonment condition can't be expressed in (at the very most!) an SQL query, it's probably too complicated to be usable. :)
What about questions that can never have an accepted answer, as they have no owner? This one has a +16 answer with a +50 bounty... I'm kinda hesitant to closing and deleting this one as well. (Other example.)