I generally buy alcohol (blush!) on the plane coming and going. It is generally as cheap as any duty free shop (limited selection, of course) on the Canadian side. MUCH cheaper than US or European duty-free shops I have visited.

I found the finest wines at Paris CDG were priced higher than the same wines at a local Mammouth supermarket in Brittany. (the wine selection in the Mammouth supermarkets is a story for another time!)

One anecdotal observation though: Some airports seem to have REALLY great seasonal sales -- perhaps they are more exposed to changing seasons, as many purchases are impulse buys.

Lately, we have found VERY few bargains in duty free stores-more often the price is more than we pay at home-taxes in. Agree with the other posters that the price of duty free on board is often substantially less than the duty free store. We just cannot be bothered lugging it home.

I usually don't buy alcohol or perfumes in duty free shops, and only once in a while on board the plane. There is such a huge choice at home and the competition often makes for better prices.

But I do frequently buy last minute gifts and souviners in airport duty free. They are usually only a little bit cheaper than on the High Street, but I don't have to lug things with me all during the trip.

For instance at LHR you have Burberry, Harrods, Liberty, Chanel, souviner shops, etc. etc. So I usually set aside most of my shopping list for friends/family for after check in . . .