I just noticed that Google has a actual frontend for Google Coupons. I was used to see Coupons being displayed alongside local business listings in Google Maps and the regular SERPS and you could search for them via Google Maps. 
To me this appears to be new but Mike Blumenthal already reported a Coupon search interface back in 2007. The search for coupons appears to have its own top URL now on the Google domain (although it is not yet available in their sitemap ) . It looks like this is yet another effort by Google raising visibility for coupons. I wonder if this will attract more business owners to get their business listed and add coupons when appropriate.
PS: It is also good to see coupons being visible/available here in the Netherlands. Google’s feature’s are mostly implemented somewhat later in Europe than in the US.
I always put a coupon on my listing and update it monthly. It’s good for getting leads and I think this lets google know I am still in business and still relevant
Jordan D