Does XCode have a cursor navigation stack like Visual Studio?
In xcode4, [Control + Command + <--] jump to the previous, [Control + Command + -->] jump to the next one.
Not in XCode 3.1.
XCode 3.2 is still under NDA, so we can't discuss its features here, but there are a lot of new features, and you should definitely reinvestigate the question when it comes out.
Yes, it does - Command + Alt + .
My XCode is 3.1.2 and it works...almost every time. It you open a new window and start working there it won't go to your previous working window. But if you change files and/or positions in files during your coding in a single window - it'll get you back.
It is called "Go Back" and lives in View menu along with "Go Forward" - Command + Alt + .
For "Go to function definition" the default key binding is Command + F12. In the menu it lives in Edit -> Find -> Jump to Definition