The changes that will come with Metro are huge--Metro apps are specialized to perform one task in a very efficient manner. Although they were designed to work with touch-screens, they also work well with the traditional mouse and keyboard. They are able to interact with other apps, even those that they are not associated with, and they will prioritize content before other issues--which is good for the end user.
The new Metro-style user interface (UI) that Microsoft has been discussing will become very familiar to everyone once Windows 8 is released. Developers need to begin to consider how they will be using the Metro-style UI within their apps, and how they will be different from traditional desktop apps, which will still be a part of Windows 8.