How often do most of us remember that "blog" derives from log, as in weblog, as in a kind of writer's notebook. The first blog so-named that I recall paying attention to was kept by a small business journalist, David Lidsky, and I've retained the notion I picked up from one of his introductory posts (as I remember it...) that a blog is a kind of public scratch pad, or commonplace book, the raw material that a writer of whatever kind compiles as fuel for more finished productions, albeit meant from the first to be public-ized.
My thought here was to spin out the analogy with the commonplace book of renaissance or later vintage, which I recall as a personal log of quotations that struck the author as worth remembering. I may have first encountered the concept in a footnote (or lecture note?) to Hamlet's exclamation, post-ghost trauma: "My tables--meet it is I set it down/That one may smile, and smile, and be a villain." -- I recall this being glossed as Hamlet thinking how right he had been to have bookmarked this jewel of wisdom when he encountered it in his studies and put it in his "tables," which are like the multiplication tables minus the multiplication, i.e. a written record meant as a memory aid.
So...checking my memory of what a commonplace book is (no free association these days is free of instant fact-check...), I find, inevitably, that its relationship to the blog has already been noted, probably repeatedly, but first in Google by a certain Lisa Spangenberg, who dredges up this wonderful definition from Jonathan Swift (get the Swift link from Lisa...):
A commonplace book is what a provident poet cannot subsist without, for this proverbial reason, that “great wits have short memories:” and whereas, on the other hand, poets, being liars by profession, ought to have good memories; to reconcile these, a book of this sort, is in the nature of a supplemental memory, or a record of what occurs remarkable in every day’s reading or conversation. There you enter not only your own original thoughts, (which, a hundred to one, are few and insignificant) but such of other men as you think fit to make your own, by entering them there. For, take this for a rule, when an author is in your books, you have the same demand upon him for his wit, as a merchant has for your money, when you are in his.