Russell mentions a Business Week report stating (the obvious):
“For U.S. consumers, it has to be simple to use,” says Tom J. Manessis, Visa’s head of emerging opportunities. “To click through six menus is not simple.”
“If a consumer has to boot up an application on the phone, and then go through four or five menus, and then choose a card to make a payment, that’s an awful lot slower and less convenient than just taking a card out of your wallet.”
I’ll say it again: yes, user interface is important. But as long as you don’t succeed in convincing consumers and merchants at the same time, the UI does not matter at all – because nobody is using it.