I only buy physical copies of books. The only exception to this is when I was in school and I'd have to take out books (especially very old/obscure ones) for assignments. But if I found it really useful, is eventually pick up a copy of it from somewhere. We have a great campus bookstore that kicks the shit out of other college bookstores I've seen. The prices rack up, so I've turned to buying used books off of Amazon for super cheap or filling in my fiction gaps from Half-Priced Books and other used bookstores. I find that, on the whole, it's not really anymore hit-or-miss than getting them new an all of my copies have been in really good, if not almost new, condition.
In actuality, the worst thing is having to find space for all of them. I have piles of them randomly in my (small ass) bedroom and computer room.