Storing Extract and how long?

How long does extract stay good? I get NB extract kits in the 1/2 gallon milk jug. How should I be storing these?

I had extract from my LHBS in a not vacuum sealed bag sitting on my basement floor for 10 months. I finally used it last weekend, and it seemed fine then. It's fermenting like it should, smells like it should and all that jazz. The concrete floor it was on is about 63*F.

I don't think I'd open one of those jugs then leave any to sit, but if they're sealed and you're not pitching yeast straight into them you should be all set for several months, anyway. I'm sure people will disagree with me, but I'm also sure the can sit for a good long time before they get brewed as well...