A few months ago, I noticed an invitation to join Amazon Vine program on my Amazon front page. I clicked on it, realized it wasn't a scam and signed up. And now I get 4 free things a month; from a limited catalog of newly released products. Mostly books are available, but I've also received software and iPod accessories. All I have to do is review three fourths of what I get and I stay in good standing.
It is awesome getting free stuff. The Phillips iPod dock/CD Player/Radio in the kitchen is sweet. But that is the exception, only the quickest get gadgets, and most of the time I have a choice between books and nothing. And getting a free book is hardly a bargain: It takes hundreds of dollars of my time to read, and I don't have the universe of books to pick from, I have whatever is in the newsletter, so I have to be picky and choose only titles which are of use—a book on business law for my wife's business—or of interest—a book on how to draw dinosaurs and aliens.
One nice thing is the motivation to read; to keep up my 75% review rate. It isn't often I read 3 books in 2 months. I just wish they offered more books about software engineering and fewer about adolescent vampires (or whatever constitutes juvenile fiction).
Amazon gets value from me. Under the theory I'll get offered items similar to things I buy or review, I bought a laptop hard drive from Amazon rather than Newegg; and I've been making sure to review anything that moves to push up my ranking. Just passed into the top 3000 woo hoo..
As to whether I'm unbiased about products I'm given to hold on to (I can't resell them), I think I'm OK. I certainly have a happy feeling about being given something nice, but on the other hand, a mediocre book is such a pain to trudge through, and a junky alarm clock just takes up space. So far, I've given out a variety of star ratings, pretty much in line with things I've purchased with my own dimes; maybe a bit lower as at least when I buy something on my own I have some expectation it will be of high quality.
Anyway, when you see the "Vine Voice" badge on a review on Amazon, you'll know it's somebody like me; just an ordinary consumer who likes to write reviews and lucked into getting free stuff.