This topic also got quite a bit of airtime on Facebook last night.
At the end of the day - some things are cheaper Duty Free, but some things are not. Do your research, and make your own decision based on the specific products that interest you.
I love wine, but almost never buy wine Duty Free as prices are usually MORE expensive than local bottle shops (South Africa is one exception). I also like drinking premium spirits. At some ports (e.g. SIN) they are cheaper than domestic bottle shops. At some ports I never buy anything (HKG, PEK, LAX, etc).
On FB drewbles reminded us that the best way to buy alcohol to take out of the USA is to visit a local liquor chain on your last day, and pack it in your checked baggage as they are even cheaper than duty free stores (even when you are paying all the associated taxes including state sales tax).