As reported by Engadget, Microsoft Engineers are working on the next project after Windows 7 for which the code name is ‘Windows 8’ and is scheduled to release in 2012. Windows 7 was released just a month ago and still Microsoft is working on different project related to that. 2009 to 2012, three years window after Windows 7 is believable as Microsoft takes that much time for an OS release.
Here is the Roadmap of Microsoft Projects where you can see Windows 8 (code name) planned to release in 2012.
What do you expect in Windows 8? What should be the major upgrade from Windows 7 to Windows 8?