My self-published novel, The Tycoon's Convenient Wife, has been on a free promotion for the last month. In that time it's had over 80,000 downloads, putting it in the Amazon UK top ten free books list. As a consequence, sales of all my other books have gone up dramatically. My next payment from Amazon should be around 40 times higher than the average payment I've received from them.
I've done free promotions before and they've never had this kind of impact. No idea why this one has, but I'm very happy about it!