Gees, you know, I did a google search for "Steem fastmine" and the first related return (2nd in the list of results) takes you to a very representative post. As you'll find, there were/are various threads on the subject, but I thought it quite coincidental that this particular post came back as my first search result. Since there is no one place where this is "documented", you'll need to research and do some reading.

Since it seems a little unbelievable, I'm going to post the google search and let you click on "Steemit how can this thing be workable long term? - Bitcoin Talk" yourself. EDIT: since the results change a bit with the link posted, I've linked the post directly. Still only just a starting point for you.

https://www.google.com/search?dcr=0&source=hp&q=steem+fastmine&oq=steem+fastmine&gs_l=psy-ab.3..35i39k1.1394.1394.0.2480.2.1.0.0.0.0.136.136.0j1.1.0....0...1.1.64.psy-ab..1.1.134.0.XykvCfNL-8s


As an aside, it's interesting to see how Steemit is actually overcoming all those initial obstacles to success that jwinterm (a long time and well respected BCT contributor) mentioned in that post - it truly speaks to just how good the base product really is. I guess the hope here is that we'll end up saying something similar someday about EOS.