Last updated October 6, 2011.
With all the names, usernames, git usernames, user.names and e-mail around, let's take a look at what they mean and where they appear.
The username set at http://drupal.org/user which you use to log into Drupal.org is, as far as it relates to Git, displayed:
On the Commitlog
On the View All Committers page
On the Maintainer's block
Your Drupal.org password, set at http://drupal.org/user, is both your Drupal.org password AND your Git password.
The Git username, set permanently at http://git-dev.drupal.org/user/[uid]/edit/git, is used for Git authentication when communicating with the sever. This is typically the same as your Drupal.org username and exists to strip special characters that create unsafe URLs and SSH usernames that may break less robust Git clients. You'll see it in:
On the Git access tab
Any e-mail associated with your Drupal.org account is a valid choice for a Git e-mail. Note that while an e-mail is associated with your account it cannot be used by any other. These e-mails aren't visible anywhere on Drupal.org, except to you on the Multiple e-mails tab.
(Your name, just like the "friendly name" displayed on an e-mail.)
This shows with user.email in the normal git commit log locally.
And it shows the repository viewer (without the e-mail).
To get credit for a commit, the e-mail you use here must match one of the e-mail addresses you've confirmed. This e-mail address will be visible in the repository's git log but is not exposed to the web (and spam bots) anywhere on Drupal.org. In addition, you can choose to use a fake address, visible at http://git-dev.drupal.org/user/[uid]/edit/git. The format is [git-username]@[your-uid].no-reply.drupal.org