If they've been well stored, I haven't noticed any degradation of bittering ability or flavor or aroma.
I used some 2007 hops about 6 months ago. I was worried about it a bit, but they were flavor hops in pellet form (crystal hops) and I did not adjust anything and they were fine. I'm not sure they would have been so great for 60 minute hops, but I would have chanced it based on the way they looked and smelled.
I have a few hops from 2012 now, and they seem fine (although only not quite two years old).