Thanks Sam. While not directly relevant, your employment is probably how you can afford to answer the questions of social-media-know-nothings like myself on the internet.
Tumblr frustrates me because I'm not 'in the stream' so to speak. The whole thing seems to be designed to just whisk you away to more Tumblrs. That could be great, but when you arrive at a page and have no clue who penned the words you're looking at or where you can go to find more of their work... it borders on infuriating.
Anyway, the reason I asked is I liked the post and found it tangentially relevant to a project I'm working on with a friend. Gave me a new way of thinking about a few things. So again, Thank You.
Yeah Tumblr can be silly. I've been into Tumblr for a while, and prior to about 6 months ago it was nearly impossible to find the original source of something without trawling through pages of "notes".
Some people put links to twitter/other social networks on their blogs but since probably >99% of the visitors to Hank's blog will get there from somewhere else in his network (Twitter, Youtube or any one of our number of community sites).
So yeah, don't feel to bad, Tumblr confuses even those of us who consider ourselves "social-media competent"
http://youtube.com/crashcourse
http://youtube.com/scishow
http://twitter.com/hankgreen
http://en.wikipedia.org/wiki/Hank_Green
(In addition to that, he's also my employer, but that might not be relevant to you)