There is a small chance, that deliveries by courier will be made tomorrow. Normally for the UK an order does not go into "Preparing for dispatch" unless it is the day of shipment. If Apple are happy for people to have their iPads from today, then they will probably allow couriers to deliver tomorrow.
Possibly, although I don't think anyone will be in at mine tomorrow so it'll be a redeliver on Friday.
I remember when my iPad 1 arrived a day earlier than launch on a Thursday, oh maaaan I was like a kid on Xmas day. That was during the brief period where I had the misfortune of being a FaceBook user (quit years ago) and I posted a stupid photo of me gurning at the camera with it. Awful behaviour,tsk.