Calibre seems a fantastic tool to manage my electronic reading, but I've had lots of problems with Calibre library management. Spent weeks getting a 10K library in shape: covers, tags, no empty formats--yahoo!

Hard drive crashed. Luckily I could recover th entire folder from a backup, but had to let Calibre restore the db (not sure why). That took some time only to find that I'm 4K books short. Had an older backup folder with the missing books--I thought, so I switched to that folder and tried to restore that db. Hours later it failed. So, thought I'd switch back only to find the first library empty again.

I've seen comments about multiple libraries, but I can't seem to keep even one working.