i made something like this but it was admin only i called it vBTracker, never released it htough.
It basicaly tied into your whos online info and recorded everything the user did as they did iot and admisn could pull up a log on what that person did.
was going to add a thing that detected how often someoen 404ed, and then pm the admin if they did it often, to prevent hackers.
but the biggest problem is this is a DB hog, it uses a lot of space in the db though it adds only 1 query a page