I have 4 bookcases in the study, so without even looking through the titles people would guess I'm a reader. As for what they say about me... probably that I'm a liberal, would-be intellectual that hangs out at bookstores a lot. ;-)
The first bookcase is all philosophy (my major in college for awhile) and religion (mostly atheism and catholism.) The second is literature; heavy on the 1850-1950 British and 1920-present American, lots of Orwell and Vonnegut. Victorian to avant garde, the shelves are overflowing.
The third case is politics, history and art. Left wing, pro-labor politcial writings. As for the histories, I love the 1920-30s and histories written by women, so that's heavily represented. And my hubby has a ton of Irish-American and Irish Republic stuff. FDR, Che, and the Kennedys have their own shelf. Art leans towards 1920's art deco, propaganda and street/graffiti. The fourth case is reference (dictionaries, guides to, quotes, etc) and essayists: David Rakoff, Sarah Vowell, David Sedaris, pretty much anyone on NPR ;-)
We really need floor to ceiling shelving put in, because there's never enough room. One of our spare bedrooms upstairs is stuffed with boxes and stacks of books that didn't make the cut to go into the study. All of the graphic novels, cook books and popular fiction is up there, (abandoned and cold in the unheated space.)