I've commented before that politicians ought to think of bloggers as more or less synonomous with 'primary voters.' I'm sure it's not a perfect guide, but I bet it's the best weather vane available. Ace talks about it here:
It's that blogs actually do, somewhat accurately, reflect public opinion. And better than polls, too, at least in this respect: While a poll might tell you that sixty-nine percent of the public is against this amnesty-without-security bill and only 20% in favor, that piece of information is, by itself, not terribly meaningful politically. Why? Because the public is against a lot of things, but doesn't really care about them. On many issues -- like bankruptcy reform -- you can probably afford to defy public preferences and give a sop to banks and creditors, because while the public may not support such "reform," neither is it politically animated about it. You can ignore public opinion because public opinion simply isn't very strong. No one's losing votes over the bankruptcy bill.
But sometimes citizens are so incensed about an issue they are actually animated to change their voting (and donating, volunteering, etc.) behavior based on a politician's position on that issue. It's not just numbers, it's intensity; and while some polls do indeed query about intensity, blogs and comments left by voting citizens are important gauge of such intensity.