These days it's hard for me to take seriously a blog post about blogging, particularly one that contends that we must take blogging seriously. Haven't we crossed that bridge about, oh, five years ago? I find it hard to believe that anyone who reads blogs doesn't understand the value of blogging.
Still, the factoid about Twitter content versus consumption is interesting: Yahoo Research found that 50% of Twitter content is generated by .05% of users. Sounds like our old friend the Pareto Principle again.
I do agree with Dorie Clark's point that writing helps one clarify ideas. Whether it also helps one demonstrate expertise is another matter entirely! I'll let you be the judge.