Most of my data was on a 5-disk RAID5 set. I'd had a hot spare for ages, but started the conversion to RAID6 to improve reliability (irony)! During the first critical phase the new disk went out, and the superblock was unrecoverable.
I reconfigured and restored 90% of the data, but the filesystem where I keep the virtual machines isn't backed up - I back up the VMs themselves. The latest VM I was working on didn't yet have a backup system (that was what I was working on) when the crash occurred. At least I know that my backup system (with the exception of the latest VM) works, there's no test like real life!