New Nexus Cards have been issued to Trusted Travelers in the US-Canada border Nexus Trusted Traveler Program. When you get a new Nexus card in themail, you will need to activate the Nexus cards before first use.
There are important issues with activation of Nexus cards. These new cards have RFID chips in them, and are quite sophisticated compared to the old Nexus cards.
The best information I have seen yet on activation is at the @Nexus.com site. They have a page that describes issues with card activation. I couldn’t figure out how to do it myself until I saw that page and learned about the http vs. https problem. See Nexus Card Activation.