A friend just tipped me to the news that Amazon has retired its Author Rank feature. (Thanks, Morris!) I'm still getting a couple reports that people are still seeing Author Rank in the Kindle Store, but Amazon has an EOL notice in the Author Central admin pages, and has disabled the relevant page in Author Central.
Originally launched in 2012, Author Rank has proven useful for little more than giving a few authors an ego boost, and many more authors crushing self-doubt. It will be missed by only the more obsessed authors and their fans.