I love Prime, but I'm an Amazon junkie. Buy a lot of stuff from them and their sellers. The free shipping alone is worth the $99 a year. Some of the things I've purchased would cost a fortune to ship. With Prime, most of those items are shipped free.
But if you are only a sporadic user, Prime may not be worthwhile. A number of third-party sellers on Amazon may offer free shipping if you're willing to wait sometimes weeks for your order.