From the http://d.wsj.com conference:
Gates just said Longhorn was affected by a year because of dealing with security issues like spam and spyware issues on the desktop. Wow. That is a big admission.
Longhorn will be available Holiday season next yearfive years after Windows XP. Gates says you want to have one year, three year and five year updates in terms of product cycles. He talked about coordinated yearly updates for Media Center, Tablet PC, and Window Media Player.
Gates added that the Media Center and Tablet support will be built into Longhorn, saying it won’t be three versions next year. Gates talked about how some folks want, for example, a Tablet-based Media Center. No brainer there.