I have to say I'm loving this. I've used it 6 times in the last 3 days - I order a few starters from one place, then a couple of main meals from somewhere else.
I haven't figured out an exact formula for getting it to work but I normally try and cover all bases by not creating a new account, giving a different phone number & email address, and also tweaking the address slightly (e.g. 123FakeSt instead of 123 Fake Street). I also use Private Browsing in Safari.
Although it is slightly annoying that some places insist on charging you 40p/50p just to use a card.