"Gustave Flaubert, proleptic critic of blog culture: "In fact, there is nothing more pernicious than being able to say everything and having a convenient outlet. You become very indulgent with yourself; and your friends are the same with you, in order that you may be so with them" (Letter to Louise Colet, 31 March 1853)."
Ouch. But of course there's irony too: it is a letter to a friend, after all.
I suppose this would only be a problem if you saw your blog as a place where you really did "say everything." I don't see that in most of the blogs I read; some are more diaristic than others, but for the most part they seem to be one aspect of a mind, one face (of many) turned towards the world, one mode of writing among others. My blog doesn't "say everything" any more than a given poem or paper I might write would.
The William Gibson quote I cited yesterday makes explicit what I think the Flaubert quote suggests: doing too much "informal" writing makes you lazy, slack, saps energy from the real task of serious writing. What seems wrong with this is that it assumes a closed economy of writing: you have a certain amount of writing energy to expend, and if you spend it blogging you will have none left for poetry, novels, whatever. I think the economy of writing is open: that writing breeds more writing.
Perhaps it's different for Gibson, a novelist who actually sells books, than for a poet, whose network of circulation is necessarily much smaller, more informal, more local. Maybe the sci-fi "fanzine" scene itself is a better analogy: a small but impassioned group with shared texts and interests, producing material that's constantly in dialogue.
And what's "safe," really, about an informal relationship with your readers? I think such relationships are much more risky than, say, simply writing a poem and sending it off to some magazine whose editor you don't know and whose readership you'll never meet. When you know your audience, there's that risk that they'll talk back, get angry, call you on something stupid that you said: what you say matters.