Revvy already posted a great link. I made a starter last weekend from yeast in my fridge that I harvested just short of 11 months earlier. It made a great starter and the beer was fermenting in under eight hours after pitching. I can be a bit lazy, but I'm pretty uptight about being as sanitary as possible. I don't think that long is recommended, but it worked for me. SO, yeast can survive quite a bit.
Kelpie Home Brewery, Lafayette Colorado
Primary: Creek Dog Stout x2, Two Dogs IPA, Grinning Kelpie Wheat
Secondary: empty :(
In Bottles: Belgian Wheat