Mardi_Gras - 2:27 pm on Dec 5, 2003 (gmt 0)

>If Cookies gives 90% accuracy

Probably more like 97%

>then it is quite possible that the 10% screws up the data massively if they are recorded at all

If the user does not acept a cookie you could still sessionize based on IP address. So then your "unknown" range drops from the 3%-5% range to a fraction of that (those users who don't accept cookies and come via proxy servers).

Like you, I am a marketer, not a tech guy. But I agree that most people don't understand how inaccurate typical visitor stats are once you get beyond basic page views.