I think for practical purposes it works better as an ID than a NEXUS/GE card as it says UNITED STATES OF AMERICAN Passport Card on the top, and lay people understand that a passport is official identification. I use it as my main ID for bars, hotels, and anywhere else. I don't think NEXUS/GE would be as accepted.
I second its use as an international ID as well. Being that it is a US Passport (card), many it tends to work well internationally where normally a passport book would be required. I prefer not removing my passport book because it is usually buried in the bottom of my bag below 14.3 other items.