I have just found
a reason to buy a Mac. This is exactly the sort of application I've wanted for years. Not just for what it does, but for how it does it, but waving the bar code of your book, DVD, CD, etc in front of your web-cam. Feck, for the first time I really wish I had a Mac.
Edit: Heh! And then a quick search determines there's a clone for Windows that's free called
Libra. Will have to have a play.