I put together a small business server system in my home office running on Win 7 x64 Ultimate (I had a license on hand not being used for anything else). It's a nice little Dell PowerEdge T20 box, which is surprisingly capable given its low price.
I set the thing up with reliability in mind, using a RAID 5 array of SSDs, internal and external HDDs for backup, and a good austere software configuration doing regular snapshots and system image backups. Powering the thing is a UPS that will keep it running for a while even in the absence of mains power. The power backup extends to the network hardware it's connected to as well.
You'd think it would be a good and solid setup, and indeed it did run for weeks without trouble.
I thought I had thought of and planned for everything. Then it went offline.
Turns out the UPS has a power button on top that's slightly recessed but not too hard to depress.
The family cat found the spot under the desk where there was a warm surface to sit on.
You can guess what happened.
No harm done, no corruption due to the unexpected power-down, and the UPS now has a nice new cover.
No cat was harmed in the making of this post.