[foghat]

I wouldn't use 3g when buying from the US store. That is the only time I've gotten messages from Amazon about being in a country different than my default address.

edit:

Figured I'd provide a bit more detail:

Thus far, I have only bought one book from the US store. This book was not available in the Canadian store. I had downloaded it via 3g to my iphone. The next day I got an email from amazon saying I had downloaded a book from a country different than the country specified on my amazon account.

Since getting my K3, I have downloaded numerous free samples via kindle wi-fi and have not received any emails.

I have also downloaded my previously bought book to my pc (transfer to pc option) and did not receive the email again.

To be safe, next time I buy a book, I will do download it via the transfer to pc option and use a US based proxy server. Though I have read that people are downloading fine without the use of a proxy.