XCode 4, Schemes & Configuration

I recently switched to XCode 4 but I’m still a bit puzzled with the changes to XCode 3.
Maybe someone here can shed some light to the following two points:

  • A minor thing, what’s the the difference between “Projectname > My Mac 32-bit” and “Projectname > My Mac 64-bit” ?
  • What’s the correct way to make a release build? The normal build (Cmd-B) seems to use the “Run” configuration (or whatever this is named in a scheme), which is “Debug” by default. At the moment I switch the build configuration in Scheme->“Run” to release, but I’m quite sure there is a better way.