Speaking at this weeks RSA conference Ben Fathi (the corporate vice president of development with Microsoft's Windows Core Operating System division) revealed that the follow up operating system to Windows Vista could be delivered as early as Q4 2009.
Windows Vista was delivered five years after it's predecessor Windows XP. This five year wait was twice as long as most people had expected the reason: Windows XP's awful security with widespread worm outbreaks in 2003. Fathi said "We put Longhorn on the back burner for awhile," following with "when we came back to it, we realized that there were incremental things that we wanted to do, and significant improvements that we wanted to make in Vista that we couldn't deliver in one release." Windows XP SP2 was released back in 2004, two and a half years after the release of Windows XP; Windows Vista was on the shelves two and a half years after XP SP2 meaning the changes in SP2 counted as a full release. I find myself wondering if we'll see a similar situation develop with Windows Vista once virus and malware coders shift their sights away from Windows XP.
After digging around a little I found some more details on the planned successor to Windows Vista; the code name is apparently Vienna. This blog over at neowin.net claims that the concept of a 'Start' menu may well be completely replaced by a new interface. The Explorer shell and taskbar are likely to be replaced entirely with the method of launching applications being similar to that employed by Apple via the OS X dock.