I've been using them for a week or so. First night, I won some cheap auctions (slightly less value than my buy in) but nothing since. I suspect the first wins are to draw you in. Overall, it's still been fun, just don't fall for the commercials; you aren't going to "win" big without spending bigger.
**Update 4/10/14: I have "won" a couple more auctions since my last review; and flat out purchased a few other things. I've still been more financially beneficial to them than they have to me, but I've come close to breaking even. I'm still waiting for most of my wins/purchases to show up (only gotten 2 out of 13 so far), so I'll update if there are any issues on that end. I don't feel like the site is a scam or rip-off, but you are not going to come out on top. Just like in Vegas, the house always wins. It is fun, though, and worth giving it a shot on a limited basis if you have money to throw away. Just don't expect to win anything expensive if you don't toss hundreds or thousands of dollars into it. I'll probably drop another hundred or so over the next couple of weeks to see if I can get something better than a 10$ gift card or 40$ fryer, and if I do, I'll eat crow and update my reviews.