Have you gotten today's update? If you have, there's a new option under Preferences in the Menu. In Behavior, check the "Home key to default screen" option. If you check that, pressing Home will take you to the screen you've selected. Pressing Home again will take you to the Expose screen preview.
I think you still have to change the default count, dont you?
The new update doesnt specify which is the home screen unless you add the proper screens in your default count.
similar to Helix 1.
unless i am missing something.