As we recently reported, Microsoft has altered its Longhorn plans to make a 2006 release possible. However, to do this many technologies intended to be a part of the OS may not be available on release - instead, they could be added in future service packs or they even might be held back until future version of Windows, such as Blackcomb.
Microsoft Chairman Bill Gates has been interviewed by Cnet New.com about how Microsoft handles such deadlines. A delay to Longhorn could hamper PC sales, or cause other problematic issues. Bill Gates talks in the interview about what changes will be happening in Longhorn to try to accomodate the 2006 release target as closely as possible.