Can NameIdentifier and IdentityProvider (WIF) claims be used to uniquely identify any user?

This seems reasonable. Note that nameidentifier is IdP specific, meaning it is supplied by the identity provider you authenticated with (e.g. LiveID, Google, etc). ACS is simply copying this value into a claim.

Check with each one of those providers to see what guarantees they make. My assumption is that they should not change for a "returning user" -> someone who posseses the same username/Password.

Justin Smith mentioned this in his MIX11 talk (see slide 22, 28 minutes into the talk) - it was my understanding that ACS gives you the nameidentifier and the IdP name. You take the tuple together and it should be good for unique id.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.