Finally calmed down.
I've been working all my SB off a USB flash drive, and managed to drop my laptop with the drive installed ... and physically broke the drive. Nothing short of microsurgery to rebuild it could save the data, so it's all dead. Fortunately most of my completed pictures that haven't been linked to SB were uploaded to imgur anyway, but I did lose a couple of completes that I hadn't got around to uploading - and my work-in-progress pictures were all lost, as is a bucket-load of reference material. Urrgghh.
So, to reiterate to all here - backup, backup, backup.