How to speedup xcode builds without any project modifications?

Question

Last version or XCode (3.2.1) is running very slow on OS X 10.6.

What kinds of tweaks can you do to your Mac in order to speedup Xcode build process.

Answer 1

For Xcode 4 this is now:

defaults write com.apple.dt.Xcode IDEBuildOperationMaxNumberOfConcurrentCompileTasks 4