In Visual Studio I can navigate backwards by pressing Ctrl + -. This is very useful when checking out the definition of a function and then immediately going back to the code I was working on.
How can I do this in Xcode? (I'm using version 3.1.2)
Xcode 3.1.x is admittedly a bit weak in this respect. Happily, the navigation @zoul mentions (The back/forward arrows in the header bar, or ⌘⌥← and ⌘⌥→) is significantly improved in Snow Leopard, and should provide the finer-grained navigation you're hoping for. Sorry there's not an immediate solution, but hopefully it helps to know that a fix is coming...