Trajano - 8:13 am on Apr 26, 2006 (gmt 0)
A ranking system mainly based on traffic patterns would led to a *STATIC RANKING* results for the most popular keywords. High traffic sites would improve thier ranking. Therefore their traffic would increase even more, reinforcing the high ranking.
On the other hand,low trafic sites would loose ranking. Therefore they would loose more traffic and finally would loose their ranking again.
It is a "retro-fed" system. You would not be able to put your new site on top, unless you get first a big traffic using other methods different from Google.