I agree about the open-source contributions, but using Stack Overflow as a metric is kinda meh...a lot of good questions are better researched (by crawling mailing lists or reading articles or even by gasp experimentation) than by going to SO. Answering questions on SO is kind of a wash, especially if you are helping your own developers and people in your community.

I also like the calling out of "I don't have time" w.r.t. contributing back. However, author is putting forth rates that are, frankly, insulting.

I like the idea of "Hey, let's reward developers that give back to their community by letting them charge more"...I dislike the metrics this author has chosen for getting there.

EDIT:

Rearranged a couple of paragraphs.