I do a lot of my shopping at Amazon, so it's a huge win. For years, I've bought all my gifts from them and just had them shipped. Lately, I'm buying household items, like coffee filters, from Amazon, too. I have free, two-day shipping, so why not?
It's $80/year, but I share it with four other people, so that's really $16 apiece.
It can be a little time consuming to look for the Amazon-Prime-eligible items, but John Hernandez just sent me a bookmarklet that winnows my Amazon searches down to Amazon Prime items.