I use my Sony 505 for almost nothing but PDFs. Even if I get a book in another format, I'll convert it to PDF. A well made PDF is better than pretty much everything else. Of course, the ideal one is one I made especially for my Sony, but even when it isn't made for my Sony, I can make it work.
I've yet to find a book or even technical journal article, so long as it is professionally made, I can't make work. (Magazines might be a different story, but who wants to read a large color magazine on a small black and white screen even with ideal zoom functionality and controls?)
The problem I think is a lot of people expect to just put the PDF onto their machine and read. You need to tweak it first. My usual tools are
sopdf and
PDFLRF. Occasionally I just use the pdfcrop tool from the TeXlive LaTeX distribution. Between those I can handle most tweaks, and since they don't alter the PDF content, they just trim margins and cut it up into screen-size chunks, nothing gets lost.