In Xcode 4, the keyboard command to commit code is cmd+alt+c. That takes you to a comparison/comment screen.
Now, when you're done typing the comment, how do you accept the commit with the keyboard? The comment field has focus, and tabbing out of it doesn't work. Return + any combination of modifier keys also don't work, as doesn't cmd+s.
Do I really have to use the mouse to commit the commit, or is there a keyboard shortcut I just can't find?
If you have a numeric keyboard use Cmd+Enter as John Yeates said.
On a notebook keyboard you can use Cmd+Fn+Return to commit.