http://us.cnn.com/2005/TECH/internet....ap/index.html

For years the press has report sites use tracking of visitors data for
advertising, and now CNN reports how people are charged according to
buying patterns.

One man claims he was charged MORE for being a regular shopper at
amazon.com.

"Amazon.com outraged some customers in September 2000 after one buyer
deleted the electronic tags on his computer that identified him as a
regular customer and noticed the price of a DVD changed from $26.24 to
$22.74. The company said it was the result of a random price test and
offered to refund buyers who paid the higher prices."

There is a good article at:
http://www.internetnews.com/ec-news/article.php/3509331 listing top
sites for e-commerce.