Great news for Diablo 3 fans who have friends all across the globe. You will now be able to play with your friends on whatever region they are playing on. There is of course some slight restrictions put in place which will stop you from doing certain things across regions.
For the full FAQ on this then head on over to the following link: http://us.battle.net/support/en/article/diablo-iii-global-play-faq.
You will have a Home game region, which effectively is your main region and this will be fully unrestricted or you to be able to sale anything on the auction house and so on. Heroes will be restricted via region, so think of it as 3 separate battle net accounts which you can switch onto for different regions. You will only be able to access the real money auction house in your Home region, this is the main reason for having a home region.
Some other good news is currently the FAQ says that it is free to switch regions, I say currently as we all know Blizzard do like to change things when it comes to payment and money.
It looks like the Korean region will not be getting the Real Money Auction house as stated in the FAQ, there will not be the interface for it. Some good news and bad news for Korean gamers, good news that they can still play the game, bad news that they do not get to experience the real money auction house.
If like me you are looking forward to Diablo 3, then now you can look forward to destroying some demonic skeletons or zombies from another region too!