The BBC magazine website has a rumination on the subject of bookcases, why we might use them, and what inferences can be drawn from them.
The writer poses a (mildly) provocative question:
But why are we so keen to show off our books – necessitating all these shelves and swelling the already bursting coffers of Swedish furnishers? Books aren’t essential – you don’t need them to sit on or eat off (unless you are a student). If you want to read, or check a reference, there are libraries.
And all those bonnet busters by the likes of Jane Austen and George Elliot – they can be called up at the touch of a mouse thanks to the numerous websites which reproduce out-of-copyright books. It’s not the same as curling up with a paperback – but how often do you really re-read the old classics?
It’s one of those things I’ve never really asked myself. You have books ∴ you need bookcases to store them in. Boxes are ok for temporary storage (although my parents have boxes of books that have been in storage since our first move when I was three years old), but books belong in bookcases. (Or in piles beside the bed, but that’s another story.) I’m going to have to start boxing some of my poetry magazines (to make space for poetry books), and even that idea makes me feel somewhat guilty … the outdoor shelving area for the Cinema Bookshop in Hay-on-Wye was quite a trial. I used to have to stare at the ground and beetle from the street to the front door without looking around.
As for the whole rereading thing – yes, I do reread my books. Repeatedly! My Pratchetts, Ffordes, and Christies would all have been read at least five or six times (most a lot more than that). Lord of the Rings I’ve reread at least once a year (on average) since I first read it at age 8. I’m what some BookMooch people refer to as a “book hoarder”. (Say it loud and say it proud!)
For those who are interested in the history of bookcases (which is inextricably tied up in the history of books), Henry Petroski’s The Book on the Bookshelf is a pretty interesting (and comprehensive) survey of how such things came to be. (If you require further titillation, chains are involved …)
To return to the original question: what do my bookcases say about me? I have no idea. (Other than the dust saying that I’m a lousy housewife, and the mess that I’m not a tidy person.) That I have eclectic tastes and a small house?
A Dark Feathered Art 
Yeah, of course the library’s going to be open just when I want to read a particular book, and naturally they will have it in stock…
And, like you, I re-read a lot; in fact it worries me that I would more often than not prefer to re-read an old favourite than explore the latest new novel. (It isn’t quite the same with poetry; I do want to keep up with the new there, but maybe that’s an urge to know what the competition is up to!)
Books aren’t essential? Well, neither are a lot of things, like clothes – that is, you really only need two sets – one to wear and one in the wash. That doesn’t seem to stop most people buying lots, and then buying furniture to store them in. The same applies to most possessions, really.
I sometimes like to borrow books from the library before I buy them, and then if I find myself going back to borrow it again and again, I realise I need to buy it.
I’m with you about the “essential” aspect – I once had a bookmark with a very apt quote from the Dutch humanist and theologian, Desiderius Erasmus Roterodamus:
Actually Erasmus had plenty of remarkably intelligent things to say, and not only about books – thanks Catherine and Sheenagh for reminding me of this quote and prompting me to find its origin!