For O'Reilly, a major technical publisher, PDF remains the most popular eBook format over EPUB and Kindle.
MediaBistro points out that OReilly's users "would want a format that resembled the print edition of a title".
The publisher's own survey found that the most popular reading device, at 46%, remains a PC, with 26% reading on an iPad.
O'Reilly's Wikert explains the results of their survey:
When you think about it, this makes a lot of sense. Again, our audience is largely IT practitioners, coding or solving other problems in front of their laptops/desktops, so they like having the content on that same screen. And just about everyone has Adobe Acrobat on their computer, so the PDF format is immediately readable on most of the laptops/desktops our customers touch.