I had a bit of a sickener on Sunday afternoon and I wanted to pause and calm down for a bit before I wrote about it. I was editing an entry in my address book, when the application suddenly hung.
I shut Address Book.app down using force quit and rebooted my machine.
All 3,600 or so contacts had vanished from address book, .mac and my phone. I couldn't find them as a hidden file somewhere using Spotlight on the Mac, they had just vanished completely.
Spooky, weird and a bit unnerving to say the least. Apple's support forums didn't reveal anything that could shed any light on this.