Thanks for all the tips!
I store mine by pressing seran wrap down on top of the dip and it stores well for several days. The guac is made with lime juice and red onion (mentioned in the video) so I bet that helps, too. I never heard of using the pit, though.
My real question was "when it starts turning brown/black, does that really mean it's gone bad, inedible?"
Mental Magpie -- that was an interesting video. At the very beginning the guy says "It's usually still perfectly edible. However it might not be something that you want to serve to company."
So I guess you could still eat it, stir it up, but it isn't very appetizing looking.