On the DVD side, identification is usually wrong when the disk you are attempting to play/rip was bought as a single, but now is available as a dual/triple. I think this is because Amazon gives preference to currently available titles. I've had several disks that the particular version I have is not in amazon's database (Kill Bill Vol 2 was the last one I ran across this problem).
IMO, I would love to see the community establish a community maintained media database. I've been using DVDProfiler on windoze for years and the accuracy, detail, and availability has been superb. Unfortunately DVDProfiler is a closed database (shareware).
With sqlCVS it should be possible to share media records. We would just need an easy to use UI and some form of media review/acceptance.
Have fun,
Roy