Kindle Book Promos
You DO get a lot of sales/action/give away. What I did wrong the first time was to put all of my books on at the same time. I'd have done better to put one in the middle of the series out, encouraging users to buy the others at full price
That said, after the service is over, you hit a weeks-long dead period and are usually a little worse off than when you started. I'd combine this with other campaigns for maximum effect.