I read lots of non-fiction science books (often filled with charts, photos, tables, etc.) and always strongly prefer those in hardbacks-- and almost always get them used through Amazon or Ebay and thus often end up with cheap (often less than $1.00 plus shipping) hardbacks with library binding and mylar slipcovers that are in very good condition (with scientific books seeing very little library traffic.)
(As an aside, many of them from Amazon and Ebay come through
http://www.betterworldbooks.com/. I've never had anything other than quick shipping of good quality books from them-- give them a try.)
For books that I conciser to be reference works that I might want to pull down at any time, I strongly prefer to have real hardbacks (but am never unhappy to find a free pirated ebook of something I already have in hardback.) For collections and anthologies of fiction, I prefer hardbacks. But for novels, I hate having to waste finite shelf space on them and strongly prefer ebook only versions and am disappointed when I have to settle for paper.