My 3e books seem fine. Covers are a little worn, from being carried about quite a bit, and some of the pages in the MM or DMG (I forget which) look like they are close to coming out -- but I think they just look that way. I've dropped 'em, and they've seen probably a couple of thousand miles of travel, but they're holding out. OTOH, I don't go out of my way to crack the spine (bending the covers back, etc.) or anything, so . . .
My original 1e books were crippled sometime in the mid-80s. The DMG spine fell apart, while the PHB's spine simply broke; I think the MM's spine broke, too, but it held out longer. My DDG is in great shape, and my Fiend Folio was when I sold it (somebody offered me $60 or $70 for it several years ago; I kind of regret selling it, though the money was handy at the time). My OA 1e had spinal problems almost immediately, and UA is still barely holding together -- about half the pages seem on the verge of falling out, though, so I only ever handle it very carefully.
Fortunately, I 'inherited' a couple of other copies of the 1e PH, DMG, & MM, so I could play AD&D 1e with no problem, should I for some reason want to.
And my first copy of GURPS Basic 3e (2nd or 3rd printing, IIRC) fell apart long ago. The cover's held together with duct tape & functions as a glorified folder for the loose pages. But that book saw a lot of (ab)use.
I guess I take fairly good care of my books, though. I do store them wrong -- stacks. I need more bookshelves...