Yesterday I reorganized my e-books (on my Nook - Calibre is a whole 'nother story). Previously, I had shelves for genres, as well as shelves for books I'd purchased, finished, reviewed, and was in the process of reading. E-books can be on more than one shelf, which meant I sometimes had books on my "bought" shelf as well as one or two genre-specific shelves.
The thing was, I rarely used the genre-specific shelves. All having my books on those shelves did was increase the number of pages my e-book collection took up and increase the amount of time it took to assign my books to shelves after I loaded them onto my Nook. So, yesterday I got rid of all the genre-specific shelves and set up shelves for "free" and "free and old" (older, out of copyright books I've gotten from Project Gutenberg and elsewhere). I'll have to wait and see how it works out for me, but I think those shelves will more closely fit how I browse through my collection. It's still better than my physical books, I guess - those have zero organization. I may catalog books for a living, but my personal collection is a mess.