I'm sure that you've been to sites that are using the new AJAX tools, one of them being the auto complete text box with a simulated dropdown list. The tool basically sends the contents of the text box to a search engine to help predict what you are typing. This in itself doesn't sound bad, until you find out what else Google is doing with this information:
http://www.consumerwatchdog.org/corporateering/corpact4/
Last night, our local CBS news affiliate asked Google exactly was they are doing with this information and confirmed that they are logging the information obtained on their servers. It's rather interesting how the most helpful of tools can be misused.