The downside of tape backup is that it's often not practical to restore from. Whenever we've had an incident where somebody messed up, it was decided that it would be less effort to spend multiple person-days rebuilding the data than it would be to restore from backup.
Yeah, it'll help in a catastrophic failure scenario, but sometimes I wish the IT guys would just turn on shadow copies or something, because tapes aren't helping with the "Oh shit, somebody accidentally deleted half the QA server, and it'd take a week to get the tape back from the archive facility, but we can rebuild it by hand in two or three days."
Meanwhile, if we'd had some sort of snapshot-based backup, it would have taken a few minutes at most.