I'm Australian and pay through a Visa debit card just fine - I did have a major issue with the card back at the start of 1.0 service however, and it took ages before the issue was fixed. It turns out it it wasn't SE's fault or even the bank's, but Visa themselves causing the problem - they had put a block on the transaction between SE and my bank mistaking it for a fraudulent transaction.

After ringing my bank about it, I was directed to Visa to get the block removed. After verifying my ID over the phone it took five minutes for Visa to remove it, and I haven't had any issues with registering or billing through the SE Account Management system ever since.