They can be had for roughly $50. That's about the cost of an AT&T SIM card on e-Bay, but with the certainty of getting one that's not a fraud. I would keep it and use it when I'm going somewhere that I don't want to take my Nexus(like the beach, offroading, etc).
Yup, when I converted my parents to ST last year, my mom was adamant about sticking to the Verizon side, and even bought a used Motorola Droid on evilbay. She was pretty irritated at me when she finally realized that you have to buy a phone FROM straight talk to use VZW. She ended up with a Samsung Proclaim. It's fine for her, but I would sooner disembowel myself than use it.
Now you can get the iPhones if you dislike freedom and love spending $$$.