On the passive voice, see: http://languagelog.ldc.upenn.edu/nll/?p=2922 and many, many more articles on that blog.
On adverbs:
http://chronicle.com/blogs/linguafranca/2013/02/20/being-an-...
and on adverb hunting via software:
http://itre.cis.upenn.edu/~myl/languagelog/archives/004271.h...
and on this app:
"The Hemingway app is fun to experiment with, and it’s useful in that it calls out in your writing places of friction—allowing you to decide whether they are necessary or merely sloppy. No one is above clarity. And the app, based on the experience of running examples of my own writing through it today, is, like a good editor, attuned to the places where vanity seems to be getting the better of things."
Having said that, computer editing will only get better, until it is used seriously by professionals.
I noted that I thought the app's logic probably wasn't "up to scratch" as is --- I'm inclined to be a bit charitable, given the direction of the criticism the app's getting.