Shifting interests, forgetting

At Many-to-Many danah boyd ponders what happens to ideas in group spaces vs. individual spaces in the context of the M2M group blog.  Specifically, what happens to a topic-centric space as the interest of the participants shifts?  Web 2.0 and Many-To-Many:

Herein lies the problem with all of this… Our lives have started to escape categories. And topical blogs are categories. Hmmm…

This inspires some incomplete thoughts for me as well.

Personal subjects in these kinds of spaces (blogs and elsewhere) tend to shift because the interests and passions of individuals change and shift over time.  And when the interests of general society changes, group spaces started around a shifting topic will either shift with the interests of the group, or they will fade away.  What becomes of the content of those spaces: is it no longer interesting to anyone? 

I suspect the topic of group spaces shift more slowly than they do for individuals.  There is more inertia in group spaces, and those who have truly moved to new ideas can leave the group.  Even corporate and government entities experience shifts, though the pace tends to be glacial (with the occasional buy-out or bankruptcy or hurricane to create faster change). 

For some reason this idea links strongly to the concept of formal categorization as opposed to folksonomy.  Formal categories are designed to keep certain ideas fixed - it takes so much effort to rearrange categorization schemes that it is rarely done.  The result is that existing schemes are expanded and bent to fit the new concepts and ideas.  (Talk to your favorite librarian to understand this in more detail.)  In the world, however, as ideas are introduced people write about them more.  With folksonomy, these emerging ideas are tagged with the appropriate terms.  The terms and ideas get more currency and build in the community, creating more interest in the idea.  At the same time, the fading ideas are talked about and referenced less frequently.  The shift happens organically.

Formal categorization is designed to prevent forgetting.  The human behavior of shifting interest is almost designed around forgetting - of acknowledging that we can only pay attention to so many things at a time.  Even in a larger community, there are only so many things that can be actively managed.  In the economy of ideas, we need to forget about some things so we can deal with others.  I wonder if folksonomy schemes enable us to do this.

I need to think about this more.  Or let it float and let others be more eloquent.