I grew up in a house where we canned out own fruit and jelly, so I have been around mason jars my whole life and love them for a number of reasons:
The lids are easily replacable. I buy one fresh box of rings every year and swap out the older ones that are showing wear. I also keep several boxes of the flat lids on hand (I don't trust a rubber seal after it's been heated, the jar leaves an impression that's hard to get out, so when I go to clean the jar, I toss out the lid).
With my vacuum sealer attachment, they create the perfect container for adjunct grains. Brewing both 5 and 1 gallon batches, I have a tendancy to over buy most of my grains (unmilled), exactly measure them on my much more accurate scale at home, and I store the extra in a vacuum sealed mason jar. (I also use them to store rice, oats, dried fruit, home grown herbs, and a few other things at home.)
I still make spaghetti sauce and stewed tomatoes to this day. And every year my mom sends jellies over (of course, she gets wine and beer in return).
They come in a number of sizes. I have the 4oz jars for my small yeast samples that I treat like a normal vial, I have pints for small starters (first steps), I have quarts for full-sized starters and yeast washing. I use a pressure cooker to jar all of my starter wort, to prevent the growth of Clostridium botulinum (aka - botulism)
The straight sided ones can be frozen. I would only use pint or smaller, as even the large mouth quarts still have a little bit of a collar to them that I wouldn't trust in the freezer.
And this is all on top of the fact that I constantly have a large selection of jars at hand, just sitting in the basement. And if I run out, I could always run out to the local store and buy a case. (I have one store that keeps them in stock all year long, and several others that stock them seasonally.)