Great post,I like your thoughts on the role/value of collaborative communities.

Quick note though: communities of purpose, unlike of practice, are resilient. In reality, traditional CoP's are a mix of shared purpose (furthering the field) and personal (being better at what I do). This can be quite volatile because the impetus behind these purposes changes, but without them being front of mind, the community deteriorates. Conscious communities of purpose adapt, or sunset.

I'm sure you'd have a few great examples of deterioration in knowledge management CoP's, for example...