I cannot read paper anymore. I'm buying the digital versions of the few ones I have in paper I haven't read yet.
Besides, nothing like cleaning my living room, all books, music and movies on a device that fits in my pocket!
Equally important is the highlight (yeah, can be done on paper too) and search functionality. Once I basically had to read the book again looking for a passage. I knew the contents of the passage, but I did not knew where in the book it was.
Some categories, like photography, design, art, etc. still don't go well in digital format, though.
DRM sucks. Not the paying part, but just how it makes our lives miserable. Also, don't understand when digital copies cost more than hard-copies (especially for text-only books).