As I mentioned above, I tried using Apple Pay at Panera and had no success because the only cash register open had no NFC terminal. But I had to get some other stuff there, so I decided to try again when they were using a different register -- this time with a "tap to pay" sign right on it. When the time came to pay, I got my phone and asked the cashier if I could use the terminal to pay. She asked me if I was trying to pay with my phone, as if I was trying to pay with my shoe or a small duck. She had never heard of Apple Pay. Her coworker at another register said that someone (I think an employee) had tried it earlier and it was cool. My cashier said that it was a bad idea, because anybody could just take your phone and go buy stuff with it. Naturally, I had to educate her a bit on how it uses fingerprints, etc. But in the end, it turned out that the register I was at also had no terminal connected to it (the terminal next to it was connected to another register). So that meant that 2 out of 4 registers had no NFC terminal, and since there's generally no way to choose which register you get, it's completely up to chance if you can use Apple Pay or not.
I know it's just the first day (although Panera has supposedly been accepting other kinds of NFC-based payments for some time). But I think this experience really illustrates one of the biggest hurdles Apple Pay will face. If it's more difficult and potentially embarrassing to trying and pay with your phone, people are just not going to do it. I felt like a real dumbass both times, and frankly I'm not sure I'm going to try again -- at least at Panera -- until they get their act together.