Google Analytics is pretty pervasive nowadays as is the Google Toolbar. Two, excellent sources of information. Google owns Feedburner, and I am sure they have agreements with other analytics companies to gather data. They are pretty much all over the place nowadays, gathering information about traffic behavior. It is fundamental to their advertising platform and their ability to deliver performance to advertisers. Google doesn't have to be perfect, just much better than their competitors, and no competitor at this time has the traffic info that Google has.
Rich
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