The 6" device, detailed here, runs Android 2.1 Eclair underneath it's proprietary UI but you can root it and have some fun, as detailed in this LifeHacker article.
Most of the main stores (Argos, Sainsburys, Asda) have all sold out already but with some detective work we managed to find it in stock at Foyles... where delivery is free and you can also get 7% cashback courtesy of TopCashback!
As we said, you'll need to get in fast, they won't be around long!
Full details on the device itself can be found at the B&N site.
Click here to view the item