Thomas wrote substantially what I wanted to write.

Edit to expand:

So some of the features of WorkMob were easy for you to write, but are not in the best interests of many people who could potentially work for you. If your design showcases to clients that "Number of OSS projects" or "Number of Github followers" are how you rate developers, your clients might actually develop the impression that those two numbers a) matter and b) matter quite a lot.

Instead of being inspired by freelance portfolios, which devote 95% of the emphasis to What and 5% of the emphasis to Why, maybe you should look at case studies by consulting firms who are good at what they do.

One I wrote which drove substantial additional business for me: http://blog.fogcreek.com/our-marketing-is-up-fog-creek-and-w...

One which I was not involved with, but which I routinely recommend for people when they ask "How do I write a case study?": http://www.conversion-rate-experts.com/seomoz-case-study/

You'll note that neither of these is particularly intensive from a features-required-to-support-the-case-study perspective. All you need is a blogging engine that lets you add images. For bonus points, email capture.