Default User Profile

In Windows XP, after customizing one user profile, many people including a corporate environment where large deployments of desktops is common used to copy that profile over to the Default User Profile. As a result, they would encounter several problems along the road that could not be duplicated with other systems without that common practice. Now that Windows Vista is available I would imagine that this practice will continue. Although I am against it because there are better ways of deploying desktops without the need for such customization of user profiles I will prepare to answer as many questions as possible because I know that their will be many.