>Any program can leave stuff laying around. If the registry entries and files were created after install, cleanup becomes very complicated, if not impossible. However, Norton is notoriously bad about leaving things around.

Sure,
but not in such sensitive areas like application start when the windows start (can't remember the right key, maybe HKLM/Microsoft/Windows/CurrentVersion/run or something like that). Or
It is not supposed to leave the changed system files (some VXDs if I remember correctly).
Thank God, they made a backups before they change these files before they replaced them.