Yup! I never knew about this until UncleR posted about it. It is a smart thing to do...you will see right there all your ADRs in black and white, so there is no wondering if there are any problems or mix ups. When I stayed at POP last trip, I had it printed for me there. It was a split stay (we were only at POP one night, actually) but I got all my ADRs for the week.
I carried them with me just in case. UncleR's story involves Upstairs at Wolfgang Pucks...they arrived for their ADR and the place was closed for a private party. He was told there was no way he had an ADR for that night. He was able to show them the ADR that he had printed out.