I used my Nexus card for the first time arriving to Canada on Sunday, May 22 at approximately 5pm at Toronto Pearson's Terminal 1. (I had previously used it in the Nexus security line to depart Canada but this was my first arrival with it.) Just wanted to share my experience. I'm a Canadian citizen who lives in Toronto.
Before landing they advised us that customs metering is in effect and that only passengers that can prove they have a connection will be allowed to leave when the doors open. Everybody whose destination is Toronto must wait until further notice. There was no exceptions available for Nexus cardholders. I was worried I was I for a long delay on the tarmac, however thankfully as soon as the last connecting passenger departed they said everybody else could leave.
After a long walk to customs I got into the line for the Nexus kiosks. All of the machines were being used and there were about 15 people lined up in front of me. The non-Nexus line was quite full but seemed to be moving well, and the end of it did not leave the customs hall.
When I got to a Nexus kiosk and had to tap my card it worked without a problem, after that it asked for my passport to allow facial recognition to be on file which I was advised would happen during my Nexus interview. When I inserted my passport the first time it said it couldn't read it, others have mentioned the same problem. I then looked at the machine and it appears you have to insert your passport quite far into the slot for it to read, further than you might think. This is why other people may have been having trouble as it's not really intuitive. If you keep getting an error saying your passport can't be read, try shoving it further into the machine. On my second attempt it worked and then the machine moved and took a new photo of me to keep on file for Nexus (this replaces the iris scans that Nexus used to use for airport arrivals).
After that I got my printout and was on my way. As I didn't have anything to declare or have any checked baggage I was outside of the airport and on the UP Train home about 40 minutes after touching down, which is definitely a record for me. I did see the new eGates but chose to use a regular kiosk instead.
Happy travels!