It's not a scam. It's data-mining and companies do this all the time. Here's how it works: no, your personal information isn't shared with anybody, that's completely correct. However, if you say in the profile "I live in a brick house with two children and a cat" and then you do a survey that asks "do you like Heavy Rain" and you click "yes I like Heavy Rain rather a lot", then that adds 1 point of "yes" to the "perhaps people who live in brick houses with two children and a cat are likely to like Heavy Rain rather a lot" part of an Excel spreadsheet somewhere. This information (to which your name is not attached) is then aggregated with all the other information from everyone else doing the surveys, and then used to conduct market research and analyse trends. The results of the analyses are then used to help companies better market products, etc. - basically, they want to know what you like, so they can sell it to you. For instance, they might find out that cat owners compared to dog owners really, really like Heavy Rain, so they might hypothetically tell the company who makes that game "hey, ever considered advertising in a pet magazine?".
They're more than happy to pay you a small sum for the surveys and throw in a few gifts here and there, because in terms of market research data, the information that you are giving them is probably way more valuable to them than a new microwave, a CD of music or an iPod dock (or whatever). Someone in whatever target demographic they are interested in at any given point in time (which would change depending on the question and who they were marketing to - which is why some of you are not getting asked anything right now) consistently doing surveys is a good thing for them.
At least they're honestly data-mining, instead of Facebook which kind of data-mines behind your back a bit. It's not such an evil thing to participate in, however I won't be because I already do lots of work and am too lazy to do this too, just for a few free gifts. I'm not sure but it seems like you live in Australia you are not paid with actual cash but instead credit on a card, which can only be spent on their gifts rather than put straight into my account. so therefore it has no interest to me. Maybe I'm wrong though, in fact I could be wrong about this entire post, but this is data-mining surveys and why they're done as far as I have always understood it. I know about it because all my employers do this too, even the tiny record label I work for on occasion has a mailing list form with "human interest" questions on it that they use for this purpose...