Should not affect home users who are not part of a domain and also should not affect corps with a second-level domain (affects third-level or more). Proxy servers, WPAD servers, and those who disable the IE 'Automatically Detect Settings' mitigate this vulnerability. Most flavors of Windows/Vista affected when using MSIE (unclear whether or not other browsers have the same vulnerability, but I would assume they do if they depend on Windows/Vista to automatically detect settings).