From what I've read you still have to report it, but the IRS isn't aware of it until you do because Amazon won't report it if it's under $600. The numbers are easy to find on your account page or itemized report.
While I am not a tax pro at all, I highly recommend making it self employed income rather than hobby. Since Amazon doesn't grant us full ownership of the items for 6 months, because they restrict our usage of them for that period in their terms, by filing it as self employed you can adjust the value to reflect the actual value at 6 months (which is considerably less in most cases). It just takes a bit of prep work to review the year's list and value each item (or set a standard 10% garage sale rate and only value the ones that deviate up or down, many go to zero if they're consumed or trash).