Well the singular on the word bookshelf was a bit disconcerting, but the conclusion for me would be that I read a lot.
Between my home and office I have about 34 linear feet (+/- 10 foot error) of floor to ceiling bookcases -- full! This does not count what I have in my rec room which is using full book cases as insulation as well as storage. What it would tell someone about me is that I have eclectic tastes. You will find Art, Animation, Computer Graphics, Web Design, Math, Physics, Computer Science, Computer Programming, assorted specific software books, Science Fiction, Fantasy, Mystery and other genre fiction. I just started with what was closest to me at this moment and continued.
On occasion people have come into my house and asked the dumb question -- "have you read all of these?". Yep! I read a LOT! but still have lots of room on the walls for art.