How does the gifts/offers thing work?

Typically, we see lots of ads on Free Laptops, Free Digital Cameras, Free Gifts, Free Offers, Free Movies  in internet where we surf. How does this thing work? Is it really possible to give away laptops, digital cameras free? When ever you sign up these sites, they take you to a lengthy survey processes. They will display various product offers which may go for 2-3 pages and ask you to give your feed back. Some sites, ask you to purchase gift cards, internet connections, subscriptions to various products and services which may cost you any were from 5$ to 100$ or more. They also ask you to refer to other friends. Only suggestion to users of these sites are- Be cautious! Do not give away your credit card details, personal information etc which may eventually leads to misuse of your credentials and accounts. So, when ever, you get into websites with Free Laptops, Free Digital Cameras, Free Gifts and Free offers etc, just sit back and see whether the site is secured.

*The above is is only the general opinion of the author.