In Xcode 4, I have been sucessfully able to add new custom keyboard shortcuts to move lines around or to duplicate a line:
/Applications/Xcode.app/Contents/Frameworks/IDEKit.framework/Resources/IDETextKeyBindingSet.plist
<key>My Custom Keys</key>
<dict>
<key>Move Line Up</key>
<string>selectLine:, cut:, moveUp:, moveToBeginningOfLine:, paste:, moveUp:</string>
<key>Move Line Down</key>
<string>selectLine:, cut:, moveDown:, moveToBeginningOfLine:, paste:, moveUp:</string>
<key>Duplicate Line</key>
<string>moveToBeginningOfLine:, deleteToEndOfLine:, yank:, insertNewline:, moveToBeginningOfLine:, yank:</string>
<key>Delete Line</key>
<string>selectLine:, delete:</string>
</dict>
But the Move Line Up/Down uses copy/paste, which I would like to avoid. Anyone knows how to move lines with yank, just like the Duplicate Line I found there: Xcode duplicate line