"As an artist that stores their art on twitter and a lot of art related sites. This troubles me deeply. Imagine if Twitter or even Youtube did this. Every video gone forever."
And just holy yikes, y'all. This gave me palpitations.
Please don't think of uploading/sharing stuff as "storing" it on any of these sites--twitter/tumblr/etc. There's no good retrieval process, you don't control compression, etc. It's nice to access stuff one's shared for resharing but not storage.