If you and your housemates buy more than two items a month from Amazon, you should consider subscribing. Be warned, though, that Prime membership will alter how you think about shopping. These days, whenever I become cognizant of some need that would ordinarily require an unplanned trip to the store—when I want a bathroom hook, a shelving system for my closet, a new wireless router, or a discount pack of kitchen sponges—I check Amazon first. It's usually faster to order the item there and get it shipped for free than to add the thing to my shopping list. With Prime, you don't really need a shopping list.
Prime membership sure will. One click and your book/item shows up two days later. How to develop bad habits.