DPAPI Managed Wrapper Library
I have written a DPAPI Managed wrapper that was pretty much taken from MSDN examples and had some extra functions added for ease of use (EncryptString, DecryptString). It uses an attribute mechanism to sandbox calls to the unmanaged functions/libraries.
The library can be found here, including full source code.
No big deal but it works well, nothing fancy, although there are rumours it can grow back amputated limbs, however I cannot confirm or deny this... ;-)