Guys, the regular promo code is (now at least) $20 for sign up ... but if you do Airbnb china...and use the automatic google translate (i have chrome, not sure if other browsers have it) you can get $40 as a sign-up.
I may have used some random guys referrel, not sure if this is vetted and will work to book and what the link is for sign up without having to use someone's referral code.