Is it really worth the cost to upgrade? I usually just order over $25 and get free shipping and although I don't get 2-day shipping, Amazon is usually pretty good about getting things to me in a timely manner.
Actually, it is to us. Our Prime membership cost $59, and we also used the $3.99 overnight option quite a bit. The only thing it is not good for is ordering items from Amazon Sellers, most of whom are not bound by the free shipping.
We feel we got more than our monies worth. We ordered several large and heavy items (Bicycle for example whose shipping weight was 72 pounds.)