I can attest to this. The sales numbers are amazing. As an author, my best title alone sold 40 copies yesterday (
MECH). When listed with the bestsellers in all SF books, not just Kindle, I'm right in there at about the same slot level as any bestseller in print. I mean that being #4 in SF adventure = #5 in all SF adventure. Logically, the Kindle books are selling faster as the print books.
Also, I've worked out with a spreadsheet that they must be selling about 100k ebook titles a day. Or more. The top 100 books are selling 200+ copies a day. A few months ago, the news was in 2009 they were selling about 10k a day. That is a 1000% growth in titles sold.
-BVL