Green Mountain, Keurig & K-Cups

Question

After a very interesting article in Newsweek last week, I bought a Keurig B60 and a bunch of different varieties of coffee. The user reviews at amazon.com were very positive on the unit.So far I have made coffee 5 or 6 times and am pleased with the unit's construction and ease of use. I am a little surprised that only the 5 1/4 oz. portion is strong enough for my wife and me.How long are K-Cups supposed to last? Any tips?