There are a couple of really handy Xcode mouse click modifier key combinations that I can never remember when I want them (kind of like a Super Street Fighter key combo).
In particular, you can click on symbols in the code editor and have them open in this editor, in the alt editor, in a new window, or... even... with a (ugly looking) popup asking you where to open (e.g. in a new tab).
Here's the lowdown:
Xcode 4 editor symbol clicks
Modifiers Click What happens
⌘⎇^ + single Open in alt editor
⌘⎇⇧ + single Select where to open (with popup)
⌘ + single Open in this editor
⌘ + double Open in this new editor window
⎇ + single Show help popup
⎇ + double Show help in organiser
⌘⎇⇧ Make alt editor counterpart again (super useful)
Key (what the silly symbols mean)
⌘ Command (cmd)
⎇ Option (alt)
^ Control (ctrl)