Instagram / Tumblr / Bitstrips / Vine are indicative of a post-literate society.
Users are avoiding processing words or concepts without imagery. The length of the facebook post / tweet is decreasing, the content - or level of content are suffering.
I'm not sure i'd include Tumblr in that list: there's quite a bit of text on Tumblr. I would include Twitter, though, which has functioned as the axe-man in the death of literate discussion on the internet.
Users are avoiding processing words or concepts without imagery. The length of the facebook post / tweet is decreasing, the content - or level of content are suffering.