According to a softpedia.com article Microsoft plans to deliver the next major iteration of Windows -known as Windows 8 - some time in the fall of 2012.

Corporate Vice President, Dan'l Lewin, indicated that it is a good guess to say that Windows 8 will go golden about a year after the BUILD developer conference. BUILD is scheduled to take place later this year. It is also possible for Microsoft to release the first public beta build around the time the conference will be held.

The interesting thing about this statement is that for the first time a Microsoft's executive is (indirectly) indicating a launch date for the next version of Windows.

Hope this is something you don't know.

Daniel stated earlier on this forum, in response to my question about when Windows 8 was to be released, that it would most likely be late 2012, so I'm not surprised.