I worked at a job where we the database outgrew the room for being able to do a restore and have two copies of the same database at the same time.
Before that had happened, we were using a third party backup software provided by the vendor knowing exactly what equipment we had and how it was set up. We did a backup and restore with no problem. Some time goes by and now the database is too large for two copies of it and we don't have another server large enough to restore a backup tape to. We updated the software and unfortunately the vendor didn't notify us or anyone at the time that their software would fail if:
1. you were using SQL Server 2000 Enterprise Edition
2. you were using Windows 2000 (some service pack, can't remember now)
3. the server was clustered
4. you were using the vendor's SQL Server agent add-on to backup SQL Server and it was a specific build.
1, 2, 3, & 4 -yep to all.
If you answered yes to all four, their product would not be able to restore the databases from the backups. Guess what, they only notified us of the issue AFTER we had a server issue and needed to restore from tape. They ended up recovering the tapes for us so we could do the restore and they 'ate' the cost of doing so, since they couldn't prove they had informed us of the issue prior to it happening.