Pretty much all been replaced by Instagram now which although has most of the same functionality the fact it's a locked in system with only the most basic form of linking and attribution makes it a completely different place for artists. People stealing work and claiming it's their own is a lot more common on IG, on Tumblr the ease of re-blogging and focus on curating allows users to flourish as either curators or creators without any bad blood between the two.
(Purely talking about the art side of Tumblr here, I wasn't involved in the other areas)