Let me throw out an alternate opinion, one which I haven't seen in the previous 100+ comments.
I'm happy this is happening. There is a lot of good non-porn stuff on Tumblr, and I will finally be able to remove Tumblr from my router blacklist without feeling tempted by the sea of porn. Believe it or not, it has nothing to do with being a right-wing or Christian or Islamic or Jewish religious nut. You see, I chose to stop using porn because I didn't like what it was doing to me, and I saw far too many studies of how damaging it is to the human male.
So I added tumblr.com to my router and OpenDNS blacklists, because I decided not to let myself wander the halls of porn on any website, and it was just too tempting to go down the wrong trails when I stumbled on a Tumblr link.
I'm sure the "damaging" thing is going to raise eyebrows, but let me explain. Don't mod me down because you disagree - I'm just hoping to pass along a lesson learned, giving people something to think about, even if they don't come to the same conclusion.
Here's what I observed about porn use in my own life. For one thing, it kept me thinking about things that were alien to my relationship with a wonderful woman who is a terrific lover already. By training me to focus on what *I* wanted all the time, it made me selfish instead of focusing on how to please her. It made me unsatisfied with a love life that was far better than as a teenager I ever dreamed it could be. It taught me to respond better to my own hand than to my partner. I realized that when I wasn't frequently jerking off to porn, my sexual response to my partner was far, far, far more satisfying, even if it took some patience and time and had the risk of not being perfectly in control. It made me unsatisfied with my partner's imperfect body, so that whenever I was enjoying her I was distracted by thinking about some imaginary set of "perfect" breasts and impossibly lithe flat tummy that were unavailable to me. Sorry, but childbirth isn't friendly to most women's bodies, and you don't see any porn stars with stretch marks. Finally, it was a huge time-waster. I got back hours a week to do better things. And all these things were born out by numerous studies that show that an awful lot of sexual dysfunction today is caused by porn, by men training their minds and bodies to respond to impossible things that have nothing to do with real women and relationships based on give-and-take and selflessness.
In short, my decision was based on real, practical observation of myself, not a religious standard. So I'm happy that I can finally have un-tempting access to Tumblr content.
Before you say "yeah, you just don't have any self-control; you're counting on Big Corporation to keep you in line." To that, I reply: For one thing, I put the block in place, and I was quite able to bypass it if I decided to do so (and I did so from time to time, despite my better intentions). It was just a simple barrier that reminded me of my own decision. For another thing, how many times have you told yourself you watch too much porn? And yet you keep at it? Sometimes, having someone else help you stick to your own decisions is a good thing. If you have such great self-control, more power to you - but you're in the minority, according to many surveys.
So don't disparage this point of view because you're better than me - recognize it may help others with what they want to improve in their lives.