Great post, Michael.
Bi-directional ties are by definition stronger than unidirectional ties, but it seems to me that whether you want weak or strong ties depends on your objectives. For example, weak ties are better for problem-solving and innovation, because your strong ties are more likely to know the same things that you know, and what you need for those purposes are people who knows things you *don't* know.
I've noticed that I personally have added more of my professional relationships to Google+, because Circles allow me to better manage them separately from family and personal friends. But maybe the support Google+ provides for unidirectional ties is another reason why Google+ is a better place for professional networks. Perhaps, like LinkedIn, G+ fiills a niche rather than taking on FB in a zero-sum game.
