How long will hops stay fresh?

Last year around this time I bought a pound of assorted hops, to get me through 2008. Unfortunately some unforeseen events prevented me from brewing as much in 2008 as I had planned. The hops were vacuum sealed and have been stored in the freezer for the past year. I have about 1/2 pound left and I'm starting to wonder if I should be worried about them going bad? If they did go bad or lose their potency, how would I know?

Depending on the hop and the way stored (vacuum packed in the freezer) you may have lost half a percent of AA% over those 12 months.

BeerSmith has a "hop age" option but I don't know what the equation is to figure that out.

Thanks mmb!