Not accurate i think because there are alot of Web 2.0 services that provide a bookmark like AddThis and AwStats cannot get that information.
Not accurate at all, I am at about 70% on one of my landing pages. It's a good page, but not that good
i think it works with checking IPs and if the visitor returns more than X times it will count them in the add to favorites! so it's not accurate, more of a guess!