Andrew Savikas posted this neat graphic yesterday. It shows a week by week track of downloads, sorted by format. It doesn't show the total number of downloads, only the percentage of the whole.
Most of the downloads were in PDF, Epub, and Kindle (the dark blue is PDF, green is Epub, and the yellow-orange is Kindle). But there is also a small amount of Android APK downloads. Very recently they added Daisy as an option; it's the tiny bit of purple in the upper right corner.
It's an interesting chart. I wonder what caused the big jump in Epub and Kindle downloads in early 2009? The only event I recall from that time was the launch of the K2, and I don't think that would have had such a big effect on Epub downloads.
One other thing. Look at the really big PDF spike. As you move forward from that point, is it just me or does the percentage of Epub downloads seem to be shrinking while the Kindle share grows?