To verify Windows 8 release time line, here's another roadmap, this time from an internal presentation from within the walls of Redmond (english). Now, with two different internal presentations in two different languages stating the same thing, it's seems to be safe to say the that ~2012 time frame for Windows 8 Server is a well-observed company-wide goal at this point. Also of note, Microsoft has finally aligned their client and server releases, this roadmap could very well stand to serve as the roadmap for the client end of things as well.