[jacknagel]

>But then I found that that email address is shared to the whole world in git commit summary!

If you're talking about the email address in the commit itself, that's part of the commit object and not anything GitHub does behind your back. If you publish the commit anywhere, not just GitHub, the email address has become public knowledge.

[user2634]

"Set up git" instructions tell this:

  git config --global user.name "Your Name"

  git config --global user.email [e-mail]

You have to use same email as in registration or else it won't push.

[getsat]

Nope. Authentication is done using your ssh key pair.

All my commits are done by [e-mail], but that is obviously not my Github email on either my personal or work accounts.