As per the title. I don't normally see many 20% off coupons floating around so may be good. Doesn't seem to have many restrictions however they do say "participating" hotels.
T&C below:
Book a participating hotel by 11:59pm (US Pacific Time) 11 December 2013, for stays between 1 December 2013 and 30 June 2014 via HotelClub iOS Apps and instantly receive 20% off your hotel booking (excluding taxes and fees). Limit one discount per hotel room and one promotion code per purchase. Applies to selected hotels only. Discounts are not redeemable for cash for any reason. Promotion codes are non-transferable and not for resale. HotelClub reserves the right to change the terms and conditions of this Promotion at any time without notification.This promo code is only valid for bookings made on HotelClub iOS Apps.
From my experience with HotelClub 'participating hotels' does not include major chains. For example I know all the Accor-brand hotels are usually excluded from these deals. No harm in trying though.