I think you may be exaggerating the significance of utility in creating trends. We all know that almost no one would be drinking anything out of those jars in ten years (just as almost no one drank from them ten years ago), while the jars will still be just as useful and just as cheap.
I've been using them for at least 10 years as the sealed top is a very convenient way to carry a drink in a lunch bag. I was a bit self-conscious about it, but now I find that I was a hipster all along!
Like most epidemics, it's difficult to trace back to patient zero. Somewhere out there was the first cool bar/cafe/whatever to start using Mason jars. They may have been doing it for years before someone else saw it and copied it. Then there were two, then there were four, and pretty soon it's everyone.
From where I'm sitting it's already a played out trend. You wouldn't catch a cool cafe nowadays using jars. But I bought some beer a few months ago and as a special offer it came with two free beer glasses. They're "jars" -- or rather, they have a thread, but no lid, and a handle like a beer glass.
