Arioste,
The best you will find in terms of market size is some educated guess'. Find transcripts from the Amazon press conference on the Kindle 2 and you will see a quote by the CEO of Amazon that something like 10% of unit sales are Kindle sales. Here is the Live Blog from Engadget and the quote as they transcribe it:
http://www.engadget.com/2009/02/09/l...ss-conference/
"More than 10% of the units we sell are Kindle book sales -- that's astonishing. So what happened? 230,000 things happened, and that's Kindle books. Even the best device without selection is useless."
There has been a lot of argument by what is meant by this figure. I read it literally that 10% of the total book sales are Kindle books. The second figure, 230,000 is how many physical books are available as Kindle (electronic) books. In other words the second figure has nothing to do with actual sales.
Even though I do read this to mean that 10% of all books sold are Kindles, I have to admit that I find this hard to believe. Search around on the capacity of the supplier of the e-ink screens and you will discover that they have capacity of roughly 500,000 per year. That means that Sony + Amazon + Irex + Cybook + Jinke + ... equals 500,000 since the Kindle I was announced. Even if Amazon is half of the total that only gives you 250,000 Kindles. I guess you could assume that Kindle buyers are all your highest volume readers, and use the Pareto rule (20/80) and that would extrapolate such that only a few percent of buyers could = 10% of all sales. However 10% does feel like a stretch.
Use google and do a search on PVI capacity of Eink. Search for Amazon Kindle sales. See what you find out. At this time, your guess will be as good as mine or anyone else's.
Michael