My friends and colleagues are quite freaked when they realise what information we get from even our basic web site analysis software at work. Broadly if we can tie one web hit to you, then we can track you pretty much forever. Our sales guys can get alerted when a prospect comes back to the web site for example.

Just imagine then what the pros can do… From RISKS:

?Date: Fri, 6 Aug 2010 16:26:51 -0400
From: Monty Solomon <monty@roscom.com>
Subject: WSJ: What Do Online Advertisers Know About You?

Tim Jones, *Wall Street Journal*, 4 Aug 2010

In a groundbreaking new series titled “What They Know,” the *Wall Street
Journal* is taking a close look at the information that online advertisers
collect about you as you browse the Web: “The tracking files represent the
leading edge of a lightly regulated, emerging industry of data-gatherers who
are in effect establishing a new business model for the Internet: one based
on intensive surveillance of people to sell data about, and predictions of,
their interests and activities, in real time.” What the industry knows
about you may surprise you. The articles examine the world of tracking
cookies, and other less well-known tracking technologies like flash cookies
and beacons. They found that “the nation’s 50 top websites on average
installed 64 pieces of tracking technology onto the computers of visitors,
usually with no warning.”

Using information gathered this way, the advertising industry is able to
accurately guess substantial information about you – often including your
gender, age, income, marital status, credit-rating, and whether you have
children or own a home. The findings are used not only to determine what
advertisements you see, but sometimes to decide what kind of discounts or
credit card offers you’re allowed access to. …
https://www.eff.org/deeplinks/2010/08/what-they-know

What They Know:
http://online.wsj.com/wtk

Online Behavioral Tracking:
http://www.eff.org/issues/online-behavioral-tracking

Scary stuff.