I don't buy books from B&N, but yes you will need to use a USA address even for 'free' ebooks and plugins.
I'd suggest also confirming/asking the store's return policy (especially restock fee) before you buy. I was actually going to return my HD after a couple of hours of playing around with it, because the non-stock android interface didn't seem ideal at the time, and I couldn't get flash to work in that limited time.
But I didn't realize there was a restock fee, so I ended up keeping mine since I couldn't get a full refund. But it's worked out pretty well, I got flash working and figured out where the wallpapers are (why they make a plain white background the default is beyond me).
I really like the screen, it's got better resolution than my laptop.
