I'm often tempted to buy my commonly used hop pellets online in bulk and storing them in my freezer. A lot of the cheap bulk hops are from the previous year. Assuming they are vacuum packed and frozen, is it safe to buy 2008 harvest hops or am I wasting my money?
It's safe if stored properly. Their bittering power will diminish with time - software like ProMash will help you estimate their current alpha acid content.
Before using them just take a whiff to tell if they have developed any cheesy aromas. You can always make a giant batch of lambic if they get too old.
As long as you factor in the loss of alpha acid over time you should be fine. A reputable supplier may even help you with the estimate.
I would also recommend that you plan to use them relatively quickly if you want to get the most out of them. So think of your next 3-4 brew sessions and work with those hops. I'd invest in a vacuum sealer yourself, to weigh and repackage these hops you get.