My numbers aren't very large, but I'd like to report my experiment with a 99 cent sale in case it helps anyone who is considering doing one.
I put the ebook version of my novel, CHOKE, on sale for 99 cents for a couple weeks in July. Before that it had sold for 5.99. After the sale I dropped it down to 4.99. When/if the sequel comes out, I'll probably drop it to 2.99.
For Kindle, the ebook first went on sale for 5.99 in May and it sold steady in May and June. During the sale, the numbers increased 66 percent and I went on to sell just slightly less at full price after that. I didn't increase income for the sale, but I got several more books out, so I'm pretty happy with that.
On Barnes and Noble, my sales were much less in May and June. The sale numbers were about double my total. I haven't noticed an increase since the sale. In fact, there are very few there.
On Smashwords I didn't sell any at 99 cents. I am, however, selling there steadily at full price, both in the US and in the UK.
When I have more books out and my numbers are larger, I'll try this again to increase readership.
Here are some links to real numbers for several authors. These aren't about 99 cent sales, but about sales in general.