I had a bunch of about two year old leftover Cascade, Columbus, Mosaic, Citra, Galaxy and Simcoe, stored in a freezer, some in unopened original packs, some opened with original pack put into a ziploc bag. I used them all in a West Coast style DIPA batch and while it was an OK beer, it was definitely lacking in fresh hop aroma and flavor. You could clearly taste that it was made from older hops.
Although now that I think of it, maybe using six different hops muddled the flavors a bit as well... (Normally I don't use more than three)