Ponibooru has shut off all uploading capabilities and will officially go dark on August 17. So if you've been keeping bookmarks/favorites of images on Ponibooru, now is the time to download them. A small sister site (http://derpiboo.ru/) has uploaded many of the high rated images from Ponibooru. So this will essentially be the 'new' Ponibooru.
You can also download torrents for all images with the link below.