I've been a An Amazon Prime customer for several months now. Amazon is truly awesome. I don't know how they do it either, but everything we've ordered so far has shown up on time, or before the estimated delivery date.
You can set up family members as well and share the Kindle stuff. I already had an account and upgraded it to Prime, then added my wife so she could get all the Kindle stuff. She's a big reader.
It's really amazing what you get for a few bucks a month. All those streaming movies, free 2nd Day Shipping, free Kindle books ... I love Amazon. We got rid our Satellite and only watch OTA and movies/shows from Amazon Prime now. So far I haven't even rented anything, there's tons of great free shows in the Prime category.
"I pulled the head off Elvis, filled Fred up to his pelvis, yaba daba do, the King is gone, and so are you."