Along those lines, I believe that mechanics design is a distinct discipline separate from both interface design and product management. I believe it deserves its own terminology, principles, processes, deliverables, and bodies of knowledge.
Really unpopular opinion for designers:
it's easier, more joyful and beneficial to do free work for someone you like, than design and release your perfect portfolio with case studies.
The only rule for free work is that you should be the one to offer it, and not asked to do it.
One mistake I often used to make at Justin.tv was offering a potpourri of business models (virtual goods, product placement, chat ads, contests, etc..). I was embarrassed to say Justin.tv would monetize with advertising when clearly that was the only answer. Own the simple business model.