Just thought I'd share my experience with this today...
We made last minute resort ressies about a week ago for this weekend. I had read about the Be Our Guest lunch ressie website on here, and decided to put in my confirmation number and see if it would work. It did, on the first try, without any issues at all. I picked our time slot, preordered our food, and double (and triple) checked that everything was confirmed.
Well, today we show up at Be Our Guest during our time slot, and they don't have our name in their system. We don't have magic bands, just our KTTW cards and our AP's. They seemed very confused, but the woman at the podium said just to go through the FP+ line anyways, but we would have to order our food again. As we were walking up the bridge, another CM stopped us and asked what we were doing. I explained the situation to her, and she was very reluctant to let us pass. I told her we made the reservation, told her the time slot, the things we ordered, etc and she eventually just let us go in. I didn't take a screen shot of our ressie (knowing what I know now, really wish I did!) and they never asked for our KTTW card or anything. We were in the restaurant, had our food ordered and were to our table in about 5 minutes. It was a super quick, efficient process. The regular line was all the way down the bridge, then turned and went back towards Gaston's Tavern. So, we were very thankful that we had made those reservations, and that they let us through without any concrete proof.
I just wanted to share this experience because I get the feeling that we just got lucky today, and usually, they are going to want some way to verify we actually had a reservation. It is very strange to me that the system allowed me to even make a reservation for this, and then we weren't on the list at all. They definitely have a lot of kinks to work out with this. I know a lot of people were worried about their reservations going through, so my advice is take as much evidence of your reservation as you can.
Sidenote: The food was SO delicious and the inside is BEAUTIFUL!