I know it sounds like there is a catch, but I've been using it for over a year without any problems. In fact, I've actually enjoyed earning a little back on so many generally un-enjoyable purchases, such as textbooks (I can rent on Chegg.com through Big Crumbs) and pet supplies (I can go through either PetSmart or PetCo among others), not to mention feed my excessive need for eBooks (through Borders or Barnes and Noble).
These are things I already would have had to buy, but through Big Crumbs I at least get the satisfaction of getting a little money back!!
It does add one more step to your shopping, but it's an easy one - you just have to go to the Big Crumbs website, then click on your desired store link from there so they can track your referral (I'm assuming that the companies that they work with pay them for their customer referrals) and make sure you get your cash back.
Sometimes the cash back is tiny, like $0.04, or sometimes it's large - I previously bought two GoChicago cards for my husband and I to use on a vacation to Chicago to visit my sister, and earned almost $16 back on the $190 purchase!! It just depends on which vendors you are buying from. You can even earn cash back on eBay purchases, which surprised me and came in handy a couple of times already - like when I was finally able to purchase a handcycle!
I know not everyone is comfortable shopping online, and some of you may still be wary. That's totally ok. I just thought of recommending this today after purchasing my textbooks for the upcoming semester, knowing that I would at least see a little bit of a return on my investment. ;)
If you're interested and want to find out more, or if you've heard enough and want to sign up, please consider clicking the link on the side of my blog, or clicking here. It lists you as a referral of mine, which means I earn a few pennies every time you shop. :) It doesn't take away from the money you earn, either.