Thanks for that!
I'm doing an experiment. I've turned it on for all drives (the data ones). Windows 7 had turned it on only for drive C, the programs drive. I'll see if I get lots more VSS errors this week.
Backup is totally automated - a DOS batchfile that creates a dated folder on the external HD and copies everything important to there. It does it while I'm asleep, early on Sunday mornings. Shadows shouldn't be needed for that.