Back in late October before I actually got my nook I was able to "buy" free books (courtesy of Google) *only* thru VPN. Back then the B&N Support had a page which explicitly stated that you need a US IP-address to buy ebooks from their store.
But recently I "bought"
this book for free without any kind of VPN with my Canadian IP address.
My experience so far is limited to free books only tho, still I hope it helps.