I tried this out briefly. The software looks pretty good, but there's basically nobody trading, which is a shame. Due to this, and because they said on the trollbox that they're not going to allow US customers in the future, I didn't actually do any trading. Deposits and withdrawals work.
I'd really like to see more option trading in the Bitcoin universe, since the "insurance" aspect of options is very useful for removing risk from end-users.
Volume and user signups are steadily growing. We did not make official statement about US customers. But for now, we are not blocking US customers. We are aiming to let anyone trade on our exchange.