In case you missed the notice on iTunes Connect, promo codes now work in all iTunes stores worldwide. http://www.macstories.net/news/finally-app-store-promo-codes-no-longer-limited-to-the-u-s/ Very nice!
This is seriously good news! Finally we can tweet to the world promo code competitions without having to always say it's only for the US (which alienates everyone else) all in 140 characters!
this will bring also some reviews of some titles to the german store. Often games have hundrets of reviews on US store but not asingle one in my store, thats really a cool move from apple.
I can confirm that this works. I've just accepted a promo code on our game from an Australian iTunes account. Worked like a charm