I know it's a bit of a "how long is a piece of string" question, but I've gone through 3 copies of Beneath A Steel Sky from ebay (original, boxed) and I still can't get a copy in which all 15 (!) disks work properly on my A1200.
It's a bit depressing really - it took me two goes to get a working Monkey Island as well. I suppose magnetic media won't last forever - at which point will *all* original Amiga software be lost to time?