Tumblr is great if you want to find entertainment and people in your fandom. I don't know much about the art side of things since I just started with the art blog, but there's a large science loving community and they're great.
The few times I've been on Tumblr I didn't like it, so I've never been interested in making an account. Plus, dA and facebook already take up too much of my life. I don't want to add another form of social media