Similar to the 3DS trade deal they had last year about this time when the 3DS price dropped
"$40 when you trade your old DS Lite, $50 when you trade your old Dsi, $60 when you trade your old DSi XL, or $100 when you trade your 3DS toward the purchase of a new 3DS or 3DS XL"
http://www.gamestop.com/collection/trade-in
I was on the fence about an XL until I found out about this deal. FYI the stores around here will let you buy the XL at full pop, go home, do the system transfer and come back with both and return the XL then resell it to you with the discount applied.