Amazon is problematic, in fact, because among other things, they don't release their actual sales figures. This means that their claims are very difficult, if not impossible to verify. According to the trade book publishers themselves, as of October 2010, e-book sales represented 8.7% of their net for 2010 (up from 3.31% in 2009 - the full figures for 2010 aren't out yet, though).
As far as what is going on in the actual e-book market vs. the print book market, it is important to note that while the product is books, the mediums are different, and there is every sign that the markets are different too (for example, e-book sales figures are not impacted by any of the peaks and valleys in the printed book market). I've been tracking these markets for a while using the data from the publishers (you can find it at publishers.org), which strike me as far more reliable than Amazon, as they actually give you numbers to crunch. Everything I've seen suggests that e-books are a brand new and growing market, with very little overlap with the printed book market. Yes, the e-book market is growing, but at the same time, it is NOT cannibalizing the print book market (with the notable exception of tech manuals and a large part of the reference market, where an e-book version is far more useful due to the ability to do word searches).
This makes a great deal of sense. The e-book is an inherently technological product, while the printed book is not. The printed book is a self-contained and simple object, while the e-book requires a technological reading device. And, it would not surprise me in the slightest if it turned out that the e-book market has its links and associations with cell phones and the cell phone app market. In fact, I would credit the increased adoption of cell phones by the public with raising the e-book market up.
Now, this leads to two main questions. Question #1 is how far up can the e-book market go? If the printed book market is only tangentially related to the e-book market at best, then the printed book market tells us very little about what is likely to happen to e-books. They could reach very high, or they could be about to plateau.
Question #2 is how badly will the e-book market be impacted by the piracy wave? This is also a question of longevity - if the e-books are representing less than 10% of trade sales, then publishers are not likely to fight to keep the market alive if piracy makes major in-roads. They are more likely to cut their losses and leave the market. So, if the piracy wave is too great, the e-book market may not survive the next five years.
(And, I would point out, a lot of major console game production companies started off in the PC game market - when the piracy became endemic in the PC game market, they voted with their feet. So, such a move by publishers would not be unprecedented.)
And, I don't have any answers to these questions. I wish I did - I'm trying to formulate an e-book strategy for my own little publishing company. Among other things, I can't find any figures for the cell phone app market, to see if they do track with the e-book market, and give a sense of what will happen next.
But, no matter what, it is vitally important for people to keep in mind that the e-book market is not necessarily part of the book market, and therefore e-book sales from online retailers tells us a great deal about e-books, but relatively little about print books.