Idea: Real-ID/Trust/Rating Network

I am contemplating a few ideas for a start-up, and this one in particular sounds really cool to me, however, being in the HN community, I know better to ask for opinions before rushing out and coding the idea.

Here are the basics...

1. Create a site that would allow users to login via each of the following networks (Paypal, Facebook or Linked in) to create an account. The more sites that are logged in to be authenticated, and compared to the other hashes, the "trust" factor increases. The final step would be to send a registered letter to the address of the account.

2. Depending on if the details of each account match, and the registered letter is received, it would issue a real-id factor (the more, the more likely it is that the user is indeed who they say they are).

3. Users can up-vote other users based on personal transactions, or even recommend with a comment. There would be no down-votes or negative comments allowed.

4. There would be a back end-api to get a rating/trust factor for other sites to implement it.

5. Users with a certain 'rank' could have dedicated email addresses with the site, as well as hot links, that would take people to a secure page to send a message to the user. I believe the second part, along with captcha would eliminate the worry about potential spam from any site.

Is this a good idea? Would you use it?