Microsoft is offering free software licenses worth $400 under the "The Windows Feedback Program", if you are aged 18+ and a resident of USA you can participate before 31 December 2007 and get the goodies (however what you will get is not clear on information page), in return you will have to let Microsoft access to your computer usage data and answer to survey questions periodically.

Microsoft websites quotes:

If you choose to participate in the survey program, you will periodically be invited to take a survey. If you prefer to give us feedback in the form of data that is automatically collected on your computer and uploaded to our servers, all you need to do is opt in to our automated feedback program and download and install our software. It takes less than 2 minutes on a 56K modem, and we'll automatically receive your feedback.