8% seems high to me as well, I don't think I've ever seen my v6 traffic over 1% honestly :(
These estimates seem way high and need support. Here is a counter-example.
Netflow on Internet 2 for last week
http://netflow.internet2.edu/weekly/20050829/
has 6.299 Gigabytes being sent by IPv6, out of a total 383.2 Terabytes, or 0.0016%
Not that I have any knowledge or expectations one way or another, but I think there is a bit of an apples-to-oranges comparision going on here. The Internet2 graphs all appear to be packets/octets whereas the other estimates were for hits to a web site, which is probably more comparible to flow counts than packet counts. I quickly looked and didn't see any flow charts in I2's Netflow site, but I'd be interested to see what percentage of I2's flow's are v6. Eric :)