Gadget blog Engadget recently single handedly cost Apple $4 billion in market cap when it published a bogus email from a supposed apple insider declaring Leopard and the iPhone were being delayed. The stock quickly rebounded but the power of blogs was evident once again.
Engadget recently detailed how it all went down. I admire them for not simply sweeping this under the rug, and it allows a reader to easily forgive them.
From the post:
So we were sitting on news of obvious importance — the email was circulating, and it was enough to set off the alarms of other sources at Apple who also started forwarding it outbound. (As it happened, we were not the only site that acquired and published that memo, perhaps just the first.) Given the nature of that news, we felt we had an obligation to inform people that Apple had sent out an internal memo in preparation of a delay in the iPhone and Leopard. And so I ran the story; I believe most people in my place would have done the same.