Find your favorite porn Tumblrs and save everything you can, because on December 17, Tumblr bans porn forever. It looks like it's because Tumblr was acquired by Verizon, and where Yahoo wanted any users they could, Verizon apparently doesn't give a fuck. My best guess is that it's hard to monetize porn unless you allow the explicit ads porn sites run, so they figured they're better off without it: they'll save money and head off any risk of Focus on the Family or whoever deciding to boycott them.
Of course Tumblr filled a niche neither other social media nor actual porn sites could fill. The article is about why 20-something women use Tumblr for porn, but I can attest that I also used it a lot, because it avoided unpleasant surprises of the sort I often encounter on porn sites. Whether the decision makes business sense probably depends on whether the porn sites attracted members who also posted and viewed advertiser-friendly content. I know that I'd been meaning to make a Tumblr account to track porn easier, which I'm not going to now, but since I can't see their ads anyways I'm no loss to them. And hey, going from the place known for porn and social justice bullshit to a place known only for social justice bullshit should really help them clarify their brand.