I think Allen got it right, in that you don't really need to keep track of your license keys until your hard drive crashes or you want to reinstall elsewhere. If you just use a password manager on your HD, do you really want to have to restore from backup to access things?
A related point: storage of notes about what you installed,how, and other configuration data. As I install software I keep a log on my old Psion 5mx PDA (obsolete but useful keyboard), with backup on my PC. If I need to set up a new machine but don't want to clone the old, I have easy, independent access to my notes.