My novel The Unicorn’s Daughter is currently free (in ebook format) at Amazon–and not doing too shabbily!
Amazon Best Sellers Rank: #1,741 Free in Kindle Store (See Top 100 Free in Kindle Store)
#4 in Kindle Store > Kindle eBooks > Mystery, Thriller & Suspense > Thrillers > Espionage
#323 in Kindle Store > Kindle eBooks > Romance > Contemporary
I know many authors, self-published and indie-published, who are opposed to free ebook promotions. “I’m not giving books away,” they say. “Why should I just give away my hard work? This isn’t a hobby!”
Why? I can think of a few excellent reasons. The main reason would be to increase readership. Most of the authors objecting to free book promotions are new authors, usually self-published, with no name recognition, no reader following. Most readers are understandably cautious buyers these days. Now that anyone can publish a book, there’s a lot of books out there that, sadly, aren’t so good.
The best thing about self-publishing is also the worst thing about self-publishing: anyone can do it. So how are readers supposed to find the good books in a sea of unfamiliar authors? They’ll be more willing to take a chance if they have nothing to lose.
Even conventional publishers have done free book promotions. Back when I was at the beginning of my career, my publisher often launched new authors with free book promotions. In the late 1980s, there were no ebooks, so publishers gave away a number of freebies–usually 1500 paperback copies. They would take out an ad in a national magazine which included a short form to be completed and mailed to the publisher. The first 1500 received would get a book by mail.
Sometimes, they would offer a money-back coupon. If anyone bought a book and didn’t like it, the publisher would refund the price of the book. That worked, too.
Berkley did a free book promo for my second novel, Angels at Midnight. I was happy to have them do it. I’m still happy to have my current publisher do free ebook promotions. I hate doing my own marketing, so anything Creativia chooses to do is fine with me. If giving away a few hundred books boosts sales for books that have been around for 10-20 years, why not?
Norma Beishir/Collin Beishir 
Yes, I’ve seen it work. I was skeptical, but the new publisher did all the work. My marketing skills are zilch.
As long as it’s limited time, I think it’s a good idea. It gets books into the hands of readers. Word of mouth spreads. That’s a win-win.
I don’t think authors should have to give away their work for free–but I also don’t think authors should have to market and promote their work. What they should have to do, and what they must do in reality, and two very different things, and that’s not a situation that will go away for most authors … so if a professional marketer thinks a giveaway is the way to go, I’m inclined to agree with them.