I just check Twitter, since Amazon's status is always a lie. My personal dashboard is still showing no problems. It's bad enough that the main public status is always green even when there's clearly a problem, but you'd think they could at least make the private status accurate.
Pretty confident that isn't it. S3 was returning InternalErrors for 22 seconds before it started timing out and/or returning 503s to all my requests.
I'd bet that something broke (causing InternalError responses) and then nodes started marking themselves as failed (causing the timeouts and 503s soon after).