Similar to the comments above about "freshness" tea loses it's medicinal qualities as it ages. If you're looking to drink green tea for it's health benefits the quality matters. Green tea that is more than 6 months old has a significant decrease in the amount of beneficial antioxidants the body can absorb. Personally I'm a big fan of loose leaf but if you're going to drink any brand of bagged teas my vote is for [Mighty Leaf.][1] They're big on flavor and high in quality.
If you're looking for creative ideas on how to use old tea I've heard they make good fertilizers and also have heard of people using them as air fresheners in their sock drawers. [1]: http://mightyleaf.com