Suggestion: change default library folder location so it's backed up by Win7 Backup
The default backup settings for a Win7 system, "Let Windows choose" does not backup non-default folders in the %userprofile% hierarchy (usually C:\users\username\. Since the default install for Calibre places the Calibre Library folder at %userprofile%\Calibre Library it will not be backed up with the '"Let Windows choose" setting for backup and one might not notice this until a backup was actually needed.
For my part, I used to add the Calibre Library folder to my backup settings along with another non-default folder I had placed in that location. Recently migrated to a new hard drive and realized it just makes more sense to place both those folders inside the %userprofile%\Documents folder so they're backed up by default.
I'd like to suggest the default library folder location be changed to be inside the Documents folder. I'd bet anyone a couple of diet Coke's that most users have no idea the default library location is not being backed up if they use the 'recommended' backup parameters on Win7. Opened an enhancement request on the bug tracker in case there's agreement this is a good idea.