When a site captures the Referrer link, how much does it know about you?

Factual Questions
1

I know they have Referrer information so that if someone clicks on an SDMB Google ad that Goole will give SDMB a brownie point.
But what if the last page you scanned was not related to the new page:
Suppose I’m on my banking site or some other site and decide to jump to a gambling site. Can that new site tell what I was looking at last? Or does that info only transfer if there’s coding in the ad button itself?

2

They can get the URL of the last page you were viewing. So, if I went straight from here to www.google.com, they’d get http://boards.straightdope.com/sdmb/showthread.php?t=354388.

3

Of course, that’s only one possible source of information a website can look at, there are a few others:

  • the internet IP address that you’re coming from.
  • the browser type HTTP header
  • Any cookies that you’ve accepted for that website
  • Any information that is specifically encoded into the link you click.
    I’m not sure if Referer information is sent if you enter a new website address in your browser address bar or click on one of your bookmarks, it might be blank in that case instead of showing your last page. For form submissions or hyperlinks, it’ll show the page containing the link or form. For images, it should have the address of the page that the image was embedded in.

I remember once, on one of my websites I used a little custom code to check the HTTP-referrer to make sure that people couldn’t steal my bandwidth and link to my images from other sites. But one of my friends couldn’t see the images on my site that way… her browser sent in a blank referrer line. We never figured out why.