Yep, this is EXACTLY how the brewpubs and even chain brewpubs did it back home. Some beer stores in the US even buy kegs/casks of speciality beers and sell them by the growler (often you sign up for their mailing list or signup to be a "Facebook friend" of theirs and you receive advanced notification of the beers that are coming in).
There's usually a pretty good discount when buying by the growler; you usually pay a deposit on the growler (although one place made me buy the growler), they stay quite fresh for up to a week, although typically they didn't last that long in my fridge. 1/2 Gallon and Gallon sizes were the most common that I saw. (2 Liter and 4 Liter).
I had growlers from 4 different brew pubs, turned 3 back in for the deposit and kept one 1 gallon growler as a small secondary fermenter for playing around with new techniques.
I absolutely love beer by the growler. Does anyone know if the legal system here in Ireland would permit it?
And maybe I'm biased but I think that refillable growlers make more sense for the companies that offer them than the disposable "take home" offerings as I think they'd give more of an edge with brand loyalty. -If you paid for a deposit on the growler that has the brewpub/brewery's name on it, AND you're a "growler club member" and you get a slight discount you're more likely to come back and get your growler refilled than you would be if you were just getting a "take home" milk carton-style growler. Then there's the obvious "green" issue of reusable glass container vs. disposable waxed carton... (I think glass growler would be more associated with a higher-end "craft" product vs. disposable carton, as well...)
Adam