...at least for a grad student.
Why? Any time I move, I have to pay to transport them. Shipping fees aren't cheap, plus packing and carrying books is a lot of work. Given that I will definitely be leaving Fairfax after graduating (cost of living is too high to stay permanently) and will likely end up moving several times after that before settling down, that's a lot of money and effort that might go into lugging paper around with me.
At first, I was hesitant about e-books. The feel of a good book in the hands is hard to replace. But, a Kindle (or other e-reader) with a cheap cover is a decent imitation, and a lot more convenient. The only real downside is inability to re-sell the book when I'm done reading.
Basically, it's time to go digital.
My new policy is to only buy paper books when (a) there's a chance I might be able to sell it later for a decent amount of cash, as is the case with a textbook or (b) the paper copy is much, much cheaper than the electronic version.
It'll be a few years before I'm moving again, but there's no time like the present to start downsizing (just don't take me out of context on that line). Right now I have around a hundred books and several years worth of National Geographic magazine. It's a paltry collection compared to some of my professors, but still more than the average person needs.
The punchline: if you want any of my books, I'll sell them cheap. Check out My Bookcase and make an offer. Even if it's low, I won't be insulted - cover the cost of shipping plus a little bit more and I'm satisfied. If you're already settled in and won't be moving soon, or don't find hauling paper to be as much of a hassle as me, then an exchange can make us both happy!