B&N is pretty serious about regional restrictions. I just tried to buy a few ebooks from B&N using a US card from overseas...didn't work. Although I could make the purchase, it would not let me download and then immediately canceled the order. So my guess is that they record your IP address at the time you click order.
Granted I tried this with free books (different rules for public domain?) but several people on the B&N site message board are complaining that they can't buy books overseas despite using a US card/address. Looks like its the petition or bust.
Btw, apparently wi-fi will only be available at B&N stores initially, but the hope is later they will open it up for use everywhere, this was reported on Gizmodo.