I am running a "old" Xcode 3 project in Xcode 4 and code sense is not working for my own classes. I have tried following:
Without any luck.
Sometimes the code sense works but mostly I just get "No Completions".
Try this:
Open Organizer then Project Tab.
Clear the "Derived Data". Xcode should re-index your project then and code sense should work. At least worked for me.