I'm always skeptical of these types of deals, but after looking into who these people were and what type of security their site offered, I felt comfortable signing up with Plink and was able to pick up a free $5 gift card to Amazon.com.
The basic idea here is that you sign up, link a credit or debit card to your account, then earn free points whenever you use that card at restaurants like Outback, Arby's, or Burger King (they've partnered with a few movie chains as well). You don't have to actually make a purchase to get the gift card though. You get 500 points just for signing up and linking a card, which is enough to get a free $5 gift card to Amazon, Walmart, and others.
I'd never heard of Plink, but they've received some decent press, have an A- rating from the BBB, and their encryption security checks out. And if, after receiving your free $5 gift card, you decide that the service isn't for you then you can delete your account.
And to boot, I got my free $5 gift card about an hour after signing up (proof). So give it a whirl, grab a few free bucks, and call it day.