greybrick, that is an astonishingly good deal if true -- but I don't see anything about it at the store's website. I'm skeptical that they would offer $90 of credit for a system that retails for $129, especially knowing that many systems being traded in would be quite old. But if that offer holds up, I might actually go for it.
There were a couple of boxes with that advertisement on them when I went in today, and the manager told me it was correct. So, for now I will assume that it is real.
Edit I just called in to another gamestop to confirm whether or not this promotion was valid for the DS lite seeing as the Gamestop I went into also made the Monster Hunter mistake. It turns out, a DS lite will drop the price to $129.99, and a DSi will drop it to $99.99. Understandable I suppose, but it was enough to put me off.
What really bugs me is that when the first gamestop pulled the boxes with the promotion details printed on them to read the deal to me, and I confirmed with them that I had a DS lite, they didn't mention the different prices. They even tried to get me to put money down then and there based on an incorrect deal. Mistakes happen, but two employees at that store both agreed that a DS lite would get me the $99 DSiXL. The things those people will say to get your money, "If I were you, I'd put down the $25 right now so that you get one and you can just bring in your DS lite when you pick it up". Hooey!