I originally posted this as a comment at ChrisBrogan.com, but since all that gets buried under the huge weight of his traffic, I though I would put it here as well.
Quality writing matters. Attention to detail — even in a blog — matters. It communicates your personal brand. Is your personal brand sloppy, unkempt, a bit disheveled and has little respect for your readers? If so, then typos, badly-formed sentences and snarky, sarcastic comments about grammar are appropriate. If your personal brand includes being taken seriously as an authority by the adults in the room, pay attention to the details.
We old dogs care about this stuff and we’re here in larger packs than you would want to believe.