I don't like PDF because Adobe control it, simply put, I don't trust proprietary technologies with something as important as information.
Open standards for ebook formats would be great. Sure PDFs are ubiquitous, but they have various licensing levels which certain devices handle to differing extents (see the Kindle). Also the software required is bloated and to an extent, intrusive. A free and open standard without licensing costs, that works on any platform is much more attractive to me.