curl -k -o ~/backups/pinboard-backups/pinboard-$(date +\%y\%m\%d).json 'https://api.pinboard.in/v1/posts/all?&auth_token=username:APItokenhere&format=json'
The backups would run while the site is live and if it ever spontaneously disappears then users would have an up-to-date backup available.