Been into my local store and they have signs all over saying that if you pre order the new DSi XL you can get it for half price if you trade in your current DSi.
The price they have for the full price is £159.99 so it should mean that you can pay £80 and give then your old DSi to get the new one.
I know this wont suit alot but someone might be interested.
There does not appear to be anything on the website yet that i can find and i notice just as a console the internet says £150 so the shop has added £10 on but seems OK to me if you are thinking of getting one.
Sorry no pictures or anything someone may have more details than me.