Originally Posted by Fbone
The last figure I remember from Apple was 180,000,000 iBooks downloaded (not purchased) during the first 9 months of 2011. They may have ended the year with 240 million, if rate continued. If Apple has less than 5% that would mean over 6 billion ebooks downloaded last year. Possible, I suppose. Or more likely Apple has a greater than 5% share and when you add in Sony, Google, BoB, Diesel, Smashwords and the others it's a higher probability. That throws off the other figures.
The OP asked about ereaders so the above doesn't answer or help him any.
One of the reasons I focused on e-reader sales is that it's a potentially knowable number (well, knowable within a regional margin of error). You can do what Ipsos Reid did in Canada, poll people and ask them what devices they have. If you ask most people how many e-books they've purchased, they would have no idea, but they can probably tell you if they have a Kobo, a Kindle, or a Nook. A clear picture of the e-book market would be really tough without the e-book sellers offering up hard numbers, and none of the majors seem excited about doing that.
That said, any hard numbers of e-books sold are interesting too, and may help us make educated guesses on how well each ecosystem is doing at garnering fans.