I traded in my 3g 16gb to them. It's been REALLY slow lately and even a restore didn't do anything to fix it so I wouldn't have really felt right selling it to someone else. Trading it in at Radio Shack, I was the first one on their reservation list and of the 1 16gb and 1 32gb that they got in on launch day, I was the only person out of around 11 people that asked for a 32gb so I got mine at launch. I walked in at 9:00, activated the phone and once it was activated, did a software wipe from the 3g and was on my merry way. The only issue I had with them was that they messed up my lines on an upgrade swap but I was able to walk into the ATT Corporate store, get a new SIM that they messed up, and walk out.
I also got the $20 accessory credit and used it for an Incipio case since it was $19.99. Although I thought it was going to just be temporary until I got a bumper, I REALLY like the case and even more that I got it for free.
Could I have gotten a little more if I had wanted the hassle of Craigslist or Ebay? Maybe. Was it worth losing a little bit to not have to worry about pricing, watching other auctions, worrying about paypal or meeting someone? DEFINITELY.