If you look in the "acknowledgements" section of any book, PhD thesis, etc., you'll find lots of authors' colleagues, friends and family members being thanked for reading and commenting on drafts of the manuscript.
Doing this for an essay on the web suggests the author has real dedication to creating a lasting work of high quality. It's probably not worth doing for a daily blog post, since you haven't put enough work into it yourself to justify asking your friends to spend time improving it. (If you keep pestering your friends to review a blog post every day, soon you'll have no friends left.) But if you're going to write the kind of longer (and infrequent) essays that PG writes, it could be feasible. You just need to write stuff that interests your friends enough to make them want to review your work.
Definitely. I try not to publish anything without at least 2 sets of trusted eyes looking over it first. Preferably more.
At any professional publication there are layers of editors. Generally the more professional the writer, the more their work is edited and proofread. In the words of E.B White "The best writing is rewriting.”
It's kind of the writers equivalent of writing tests (and code review). The good ones never ship before running them.
