When - and why - should you store data in the Windows Registry?

If you are developing a new app and you care about portability you should NEVER store data in windows registry since other OS don't have a (windows) registry (duh note - this may be obvious but gets often overlooked).

If you're only developing for Win platforms ... try to avoid it as much as possible. Config files (possibly encrypted) are a way better solution. There's no gain in storing data into the registry - (isolated storage is a much better solution for example if you're using .NET).