It seems that GameStop locations are going to vary with their treatment of the 3DS to 3DS XL trade-ins. As I've said, my local store said a $100 trade-in deal is on the way. They also told me that customers can do system transfers, so long as the store isn't too busy.
Unfortunately, we've been hearing that some locations aren't going to allow for the system transfers. That's going to be quite a dealbreaker for some consumers. Just give your local store a call and see what the situation is before you plop down your cash. Thanks to Jeff for the heads up!