Used Apple Pay a couple of times this week running on a old Nationwide account. Worked well without any issues. The Marks & Spencer cashier was slightly confused when I held my iPhone up to pay. Can't have been many people used it yet I assume.
My main bank (Lloyds) really needs to hurry up and support it.
Tweet them @AskLloydsBank. If enough people get on to them they may pull there finger out.