Having said that, the only books in my collection that have lost their covers are US paperbacks. Go figure!
The US has at least two different major kinds of paperback bindings. There's a "mass market paperback" that is physically small (i.e. half the footprint size of a hardcover). They tend to use very cheap paper and cheap bindings, usually apply to popular books of 300-900 pages in length, and aren't very durable. Then there's a trade paperback, or a literary paperback, that's usually closer to the size of a hardcover, uses paper of comparable quality to hardcovers, and has a nicer binding. They're used for a few things, but the biggest area is "literary" fiction, usually consisting of books of 150-250 pages in length, although I have dictionaries, etc, in this format. They can be very nice. Some of them even use nicer paper than most of my hardcovers!
That being said, I prefer buying used hardcovers to new paperbacks, when I can.
Of the foreign paperbacks I have laying around, a couple of French ones look like mass-market US paperbacks (and they're both things that would have sold in the other format here); the ones from Russia and India vary from close to TPB to worse than MMPB.
