If I live in Australia/New Zealand/Southeast Asia, what server will I play Diablo III on?
Diablo III players in Australia, New Zealand, and Southeast Asia will, by default, connect to the Americas region. By connecting to this region, players will have a wider pool of people to play with and access to a more vibrant and active auction house marketplace. Further details on regional connection options and auction house functionality will be posted at www.diablo3.com prior to release.

How does this impact the items I have purchased in the auction house?
Auction house purchases are bound to the servers in the region in which they're bought. Any items acquired on game servers in the Americas region are bound to those servers and are not transferrable to the servers in Europe or Asia (and vice versa). Please keep this in mind when making purchases in the auction house. We’ll release more details on the auction house functionality prior to the game’s release.