It's legit, you just have to fill out a ton of surveys and probably subscribe to a couple of services. I wouldn't do it though, you'll be inundated with junk mail and telemarketer calls...although you will have your PS3.
TB's link is different though, it's offering you a PS3 for an actual price. The ones you're talking about always advertise as free.
FAQWhy is this Playstation3 System so cheap?
We get paid through our network of sponsors for every survey you fill out. This gives us the purchasing power necessary to pass these large discounts on to you.
"If it's too good to be true, it probably is."