The evolutionary sequence is:
1. Facial expressions and vocalizations.
2. Language (speech and writing).
Each makes clearer to everyone else what is inside us. Human nature being what it is — closely tied to occupational specialization — it should be no surprise that blogging is very useful in getting a job, as Penelope Trunk says. To get a job you need a skill. Your skill is inside you; blogging makes it much more apparent. Blogging shows not only that you have a skill but that you have an emotional attachment, too: Bloggers write about what they care about. Not only does blogging help you get a job, it helps you get a job you want.
There should be software that creates networks of blogs based on similarity. I wish I knew which blogs were most like mine, for example.