My comment was incomplete. While tumblr does a great job of stifling the average user's ability to POST anything "sexy", they seem to have zero ability to manage porn bots. I believe they are intentionally letting porn pots run free in order to sustain user base. Porn bots jumped again after they brought out new community standards last fall or early this year.

If you're just a porn consumer, it's fine. If you want to post porn and you know how to evade tumblr's detection schemes, it's great for you.