Used it first in the restaurant at work - it worked perfectly. The server was extremely bemused at my suggestion to pay with my phone at first and she closely examined the receipt when it printed.
When I tried at Waitrose my phone said it had worked and showed the amount paid but the payment terminal and recognise it and continued to prompt for payment. I reauthorised and it worked.
Morrisons was a disaster. TouchID recognition failed - probably due to sweaty fingers - and then when it finally did work the system went into processing mode and eventually the transaction declined. Again the phone said it was a success. Not sure what caused this seeing as it should work everywhere but Morrisons saying on Twitter that they will support from tomorrow. The slightly rude self checkout assistant tried to tell me that it was Apple Watch only.
It worked perfectly at Boots, M&S and Tesco.
Next time I'll go to the main checkout rather than self checkout to experience more bemusement from the checkout staff.
I did notice a non-detrimental delay compared to contactless card due to online authorisation.
Same happened to me in Morrisons, I just put it down to their Self Checkout machines being useless. I can't see that they are going to change anything to support it tomorrow - they are so behind with technology I am surprised they even accept Contactless.