Chris Green, a Microsoft employee has placed information about the release dates of Microsoft’s next products including Windows 8, Windows Server 2012 (Windows 8 Server) and Office 2012 on his MSDN blogs.
According to Chris:

“The content of this site are my own personal opinions and are not intended to represent my employer’s view. These postings are provided “AS IS” with no warranties, and confer no rights.”

Windows 8 Release Date:

RTM: Friday, July 1, 2011

Mainstream Support: Friday, July 1, 2011 – Thursday, July 1, 2016Extended Support: Friday, July 1, 2016 – Thursday, July 1, 2021

Windows Server 2012 (Windows 8 Server):

RTM: Monday, July 2, 2012

Mainstream Support: Monday, July 2, 2012 – Friday, June 30, 2017Extended Support: Monday, July 3, 2017 – Friday, July 1, 2022

Office 2012 (Office 15):

RTM: Monday, July 2, 2012

Mainstream Support: Monday, July 2, 2012 – Friday, June 30, 2017 Extended Support: Monday, July 3, 2017 – Tuesday, July 5, 2022