Coming from Eclipse and having been used to duplicate lines all the time, it\'s pretty strange finding out that Xcode has no such function. Or does it?
I know it\'s
Use user scripts.
There are scripts to move and delete lines yet. You have to define key binds for those scripts (menu Scripts -> Edit User Scripts..., under xCode 3.2).
To duplicate line, you have to make your own script. But it's very simple ! Duplicate the "Move Line Down" script and remove the line which delete selected text :
delete (paragraphs startLine through endLine)