Aspiring international auction house tycoons may still be disappointed.
While 2010's StarCraft II was a tremendous commercial and critical success, one of the (many) complaints that hardcore PC gamers had with the game was that Blizzard's Battle.net service did not support fully international play. If you bought a North American copy of the game, you were playing with other people on the North American servers, period. Blizzard has announced that Diablo III will not be bound by the same restrictions and will let players adventure on any regional server they so chose - with a few caveats, mind you.
The crux of the matter, of course, is that Diablo III will (in)famously feature a real-money Auction House for players to buy and sell in-game loot. Quite understandably, Blizzard is wary of letting players become international in-game tycoons by buying items in one region and selling them in another (not to mention that it probably would be violating some laws somewhere).
So here's the skinny: While you will be able to switch to any of the game's three global regions - Europe, the Americas, or Asia - at any time before or after logging into Diablo III, your characters, items, and friends lists are server-specific and won't come with you. Ergo, no matter how badass your level 58 barbarian on the American server may be, if you want to play across the pond you're going to be starting from scratch. Since Diablo has always encouraged constant replay, this isn't as much of a pain as it might sound.
Furthermore, while your characters will be able to use the in-game Auction House in whatever region they call home, you'll be stuck using plain old in-game gold if you aren't playing in the region that corresponds to the location on your Battle.net account. If your B.net is registered to someplace in Taiwan and you're playing on the US servers, there'll be no real-money auctions for you!
Speaking of the real-money Auction House, Blizzard has updated its FAQ on the subject with some more details about pricing, policies, and whether or not the developer will ever directly sell gear to players itself (hint: it won't).
The Diablo III solution is worlds better than the paltry limited cross-region play Blizzard rolled out for StarCraft II, and one can only hope that the PC giant will be adding this functionality to the sci-fi RTS either in a patch or with the release of Heart of the Swarm. That is, provided the developers include an option to opt out from being totally destroyed at the hands of somebody playing from Seoul.