[Tim Wood]

You no longer need to do this in Xcode 4; it automatically segregates build products from each workspace in ~/Library/Developer/Xcode/DerivedData. Instead, you need to make a workspace with the appropriate projects as members (along with your other app/framework targets).

If you are just checking out one of the iOS sample apps, you should be able to just open it and build (since those already have project references for the frameworks and Xcode 4 follows those).