LaDan wrote:how much air can it really suck out of a hard walls jar?
Did a little googling (http://pump-n-seal.com/comparison.htm
), and it appears that the Tilia Foodsaver can pull about 24.2" Hg - then doing the math (24.2" Hg = 0.81 atm) you would expect almost 20% of the air to still be in the jar.
I'm not a canner, but I assume the purpose of the vacuum in canning is to insure a good seal, and also to let you know if you have a failed seal - not so much to remove oxygen.
For frozen mason/ball jars, you have verification of a good seal without any vacuum shenanigans. When you take a jar out of the freezer it should be under vacuum (because of the temperature) and you will hear the lid 'ping' when it warms up if the seal is good. This is true in my experience even for beans only a day out of the roaster.
What I sometimes do (which may be silly overkill) is to stick the nozzle of my wine preserver (inert gas) under the lid and give it a few blasts before sealing the lid and freezing. Idea is that less oxygen in there is probably a good thing. I happen to have a can of wine preserver handy on my counter, otherwise I probably wouldn't bother.