It is best hung but will still be effective hen laid on a surface.
Daniel on Salt Water Cure Feng Shui
There is no difference between hemisphere's in the advice we write as your south would also be the south that we write about.The advice we give is only a general guideline to help make the most of good aspects and avoid the negative ones; there are many circumstances that can cause problems and sadly, we are unable to advise on these without a personal visit.
I hope this helps clear things up.
Daniel on Feng Shui Blog