The AAP released their sales figures for April 2011 and the is quite fascinating. The AAP's member publishers reported that ebook sales for April totaled $72.8 million, and hat's up a smidgen from March 2011 ($69.9 million) but still down from February ($90.3 million). Print was down in most categories but 20% or more, which makes the ebook figures impressive.
I continue to track and plot the sales figures, and so far it looks like my prediction about a Christmas-related bump and a series of plateaus is staying true.
BTW, I expect another bump in sales in the June figures (or possibly July). Both B&N and Kobo announced a new ebook reader at the end of May, and I suspect that the market growth is largely driven by product launches.