Anyone ever used listia.com before?

I came across listia.com a week or so ago. It's a web site where you put stuff up for auction, but instead of using money to bid, people use credits. You can then use your credits to buy things on the site from other people. Most of the auctions I saw had free shipping, but I think there is an option to have the buyer pay shipping costs. I signed up and got around 500 free credits and quickly won an auction for the 2 Randy Johnson cards below. Not too shabby, since I got them for free. I recieved them in the mail a few days later. It's kind of a cool concept. Not sure how much I'll use it though. If you've used listia before let me know what your experience has been. Thanks!