Source: (VP Online Technology Blizzard/Diablo3 from 10:00 to the end)
To sum up relative to regions:
- Diablo 3 is region free, you have a default region (based on your address) but it can be modified to play in another region (think D2).
- You can use every gold-ah
- You are restricted (locked) to a specific Real Money AH based on your address when you activate your game
- You may move region providing proof of habitation (not 100% sure).
- These apply for EU/NA 100% some things may be different for Asia.
It's not said if characters are locked in the region you created them. I would assume they are, otherwise you could transfer items from one RMAH to another and make profit through money exchange and anyway destroy the purpose of locking you to a rmah region.