Yeah, I haven't done it yet but if the value holds for the week I'll likely trade my copy in on the weekend. Tuth be told there's no reason to keep it around and if I can cost SE/CD a handful of dollars by someone buying my used copy I will gladly do so. (Maybe next time they do some decent tombs.)
It dropped from $25 to $24 base at Gamestop yesterday. Without any other promotions, you can get over $30 if you put it towards another hit game out now or coming out soon (there is a list of 8 that get 30% bump.) I think it's still $36 base at Amazon.