I cancelled my Prime membership (after 10 years) last week after spending 2.5 hours on the phone trying to figure out where a package 2 days past it's guaranteed delivery date was and if it was going to arrive or if I had to re-buy it.
I have no regrets about it. Everything I bought on Amazon I can buy from other websites, and when I have an issue I don't have to spend hours verifying my name and address with someone whose accent I honest to god can not understand (I am not a native American, it is very difficult for me to understand Indian accents).