What program, if I may ask? I've been using Delicious Library, and it's got some pretty good features, including using an iSight to scan UPC codes. But I'd like something that does a better job with books too old to have a UPC (of which I have a lot), especially if it can do ISBN lookups and check against the Library of Congress.
That's the one. I've also found the Amazon-only lookup limiting. But I do like that it checks Amazon Germany for my German books. It also can't look-up paperbacks well using the scanner. Still, it's the best thing I've found so far, 367 books inputted (probably 3/4 successfully with the scanner) and I've barely started.