Digitimes is predicting ereader sales slow their growth in 2012 (globally) vs. 2011 to only 31.4% YOY growth. That link is also predicting that Amazon's share:
2011: 73.7% of 22M ereaders.
My comments: For there only to be 31.4% growth after 100% growth year after year doesn't make sense. Market penetration tends to be symmetrical until a new technology displaces the old. Considering how many new buyers of the lower cost Kindles are coming out of the woodwork, I expect far faster growth in 2012. But... I also expect 2012 to be the last year of fast ereader growth.
It takes 2 to 3 years of ereader sales in a region to stimulate the growth. Book readers want to see their friends try out an ereader before they 'give up the smell' of books. The K1 was launched in 2007; we've yet to see more than about a quarter of books selling via ebook (in dollars).
I'm also very bullish on Amazon doing well in India (due to the quantity of people there who have the ability to read in English). With the new Kobo buyout, I'm also more bullish on ereaders in Asia (Japan in 2012, but all of Asia in the next 5 years).
My prediction is 45 to 55 million ereaders in 2012 (global prediction). I also predict, in 2012, that about 25% of the growth in ebooks will be via tablets (Kindle Fire, iPad 2/3, Nook Tablet, other tablets). In my opinion the rapid growth of ereading on cell phones is coming to an end. Oh, I predict new readers will still try out the Kindle app on cell phones and existing ereaders will take 'convenience reads' on their cell phones. My opinion is based on how many people are switching from reading on their cell phones to ereaders or tablets. 7" tablets are small enough to tote around (10" tablets are not... trust me. I made the mistake of lugging our iPad around today).
I wonder how the overall ebook market share will go. I'm waiting to see how the Kobo buyout works. IMHO, that could be the #1 global threat to the Kindle.