Let's create community extension that would allow login to Magento Backend with most popular (and some more) OAuth providers:
- Google
- Facebook
- Twitter

What more providers could be added?

The idea is very simple - once you have a Magento admin user with the same e-mail than is your Google/FB/Twitter e-mail you should be able to sign in to backend without entering your password.

It's useful for 2 reasons at least:
1) increased security - no need to enter password over possibly unsecured (non-https) connection
2) convenience - it's very much more convenient to log in with OAuth than a password

I have some version of this extension ready. It needs further testing, support of additional OAuth providers added + possibly a lot new good features.