With Windows 7, Microsoft is making some subtle changes to the ways it tries to thwart piracy.
As has been the case for some time, Microsoft's strategy hinges on requiring a user to electronically verify their copy of the software, a process known as activation, and then the software also periodically validates that a copy of Windows is genuine.

In Windows Vista, if a user does not activate their software immediately, they get a warning that they still need to do so. The dialog box offers two options, to activate immediately or to do so later. However, the activate later box cannot be checked for 15 seconds.

Microsoft decided this was a bit too annoying. With Windows 7, users can click activate later immediately, but then get a dialog box touting the benefits of activation.
More at; http://news.cnet.com/8301-13860_3-10234441-56.html