Big Crumbs??

So I stumbled onto this website and thought it might actually be a good thing. Apparently you can make a kind of 'commission' when you shop online. All you have to do is go here and sign up, then just shop! You can shop Walmart, Target, Ebay and hundreds of different stores. Then in a month or so, you'll get paid a percentage of what you've spent. I haven't really tried it out yet, but I'm all signed up. It's completely FREE! I figured since I'm going to shop online anyway, why not get a little cash back from it! Has anyone else heard of this?? I did a little research and found there are a few different ones out there, but it seems most people like Big Crumbs. Take a look and let me know what you think! I'm curious to see if anyone has used it and what they think about it.