For a while I administered a department-level "server" (basically, a large and noisy workstation) running some flavor of Windows (I think Win 2K). Colleagues in my department used it for assorted purposes, including research (web-based surveys), and like all good users they (a) never deleted anything from the server (since, from their perspective, space was free) and (b) were cavalier about maintaining their own copies of their files. When the time came to retire the server, I sent out a couple of warning emails (get your files or wave goodbye to them). I also created a ZIP archive of all data files on the server before turning it into a doorstop.
Recently (meaning a couple of years or so after the server was recycled) a colleague asked me if I could recover her surveys and survey data. So I scrounged around and found the ZIP archive ... only to discover that it cannot be decompressed by any program I can find. I've tried at least seven alternatives, including the compression/decompression method built into Windows 7, several popular third-party programs for the Windows platform, and gunzip on Linux. They all show the contents of the archive correctly, and they all fail (either with an error message or, in one case, by freezing) when I try to extract anything from the archive. The error message is that the compression method (described by the ordinal 18 in some cases and the name "IBM/Terse (new)" in others) is unsupported.
Up to now, I've naively assumed that a ZIP file is a ZIP file is a ZIP file. I know that what's being zipped could be a TAR archive, a bunch of files or whatever, and I know that some ZIP utilities give the user options for trading extra time for smaller file sizes. I've never had an uncorrupted ZIP file fail to decompress using any compression program, whether the same one that created the archive or not ... until now.
In the future, I guess I will need to be extra careful about how important backups are compressed -- and hope that the compression method used does not go the way of the card reader.