I always use the duty free for liquor. I just picked up a 1l bottle of Bombay Sapphire on an AC flight for $23, 750ml at the LCBO runs $28. So not a huge savings, but eh, it was a late flight and I wanted gin for the weekend.

I do pretty much just treat it as a convenient liquor store on my trips back. It's honestly not worth my while to go out of my way for duty free shops as they're not THAT good of a deal, but if I'm out of vodka or whatever and don't have time to head to the LCBO on my way home from my flight, why not take advantage and save a few dollars.

Best deal was probably a 1l bottle of Hendrick's gin (my favourite) for $33USD. 750ml at the LCBO runs $43.