I was very highly impressed by Google Mail a moment ago.
A relative sent me a mail informing me of a FedEx package he delivered to my parents' house in Ottawa. In the mail he included the following line:
The FedEx tracking number is xxx and its details can be found on the net (http://www.fedex.com/Tracking)
Of course the real number was in place of the xxx. There was more to the mail, besides this line, both before and after it. It was all of a personal nature and didn't talk about the FedEx delivery.
However, Google's Adwords seemed to have parsed the text of the mail so well that it detected the tracking number and the fact that it was a FedEx tracking number. It then provided me with an unobtrusive ad message and link saying "Would you like to track FedEx package xxx". I clicked on the link and it took me to the relevant tracking page on the FedEx site, with all the tracking details.
I thought it was pretty amazing. At the same time, I'm not sure I am crazy about my mails being parsed and analyzed to that extent.