This is no more rumor know as the premier rootage of Windows 7 Builds leaks the Windows 7 Service Pack 1. As the news spread like a fire to blogosphere and torrents sites. So finally the Windows 7 Service Pack 1 Build 7601.16556.
From build up count it appears this build from Windows 7 SP1 was piled up during 21st April 2010. There are no major changes in the new build release except the bugs issues have been fixed out. The giant advantages will be gained by Windows Server 2008 R2 users. Here are hashes from Windows 7 build up 7 Build 7601.16556.100421-1510 SP1.
BUILD: 7601.16556.100421-1510; Service Pack 1, v.172
SIZE: 1,306,019,840 Byte
Wzor has also published the roadmap details of Windows 7 Development process which are as follow,
4/14/2010 - Beta Release!
4/12/2010 - Beta Release to HTP RTM
4/14-6/11 - Beta Deployment and Feedback
5/10-5/21 - Win7 BTP
6/07/2010 - HTP RTW
5/17-6/11 - RC FTP
6/21/2010 - FORK RC