There is a company that advertises a website visitor tracking system
that uses "remote tracking."  Remote tracking is defined as...

"...the ability to track activity on a website you promote, but that
you don't own. Up until now, all you could do is send traffic to a
site, and know how many visitors actually got to the site. With
(product name) - you have the ability to track what YOUR traffic did -
all the way to the point of a sale."

So essentually, a remote tracking system tracks a visitor through a
website without adding code to the website pages.  The only place you
could pass any information is through the referal link to the website.

Also -- We have confirmed that Remote Tracking does not use cookies.

How does it work?

Check this out:

http://www.privacy.net/analyze/

Thats just an example, your browser tells a lot to the other side,
including your IP, which you came from, what session is your windows,
what plugins you have etc... the server can track users by IP, or
browser etc...

Also notice during all these clicks... all of them are logged etc...

You get the idea :)