With Windows 7 not due for a few weeks yet, Microsoft has (inadvertently?) leaked information about the upcoming Windows 8 and Windows 9. In case you aren't able to view the page at Google's cache, a LinkedIn profile for a Microsoft senior research developer says:
Working in high security department for research and development involving strategic planning for medium and longterm projects. Research & Development projects including 128bit architecture compatibility with the Windows 8 kernel and Windows 9 project plan. Forming relationships with major partners: Intel, AMD, HP and IBM.
So now we know, Windows 8 will include 128bit support. Or will it? We've seen this kind of thing from Microsoft before: leak, announce, hype, delay. WinFS, anyone? That was announced as far back as 2003, intended for Windows Vista. But that got pushed to Windows 7. Then, it got delayed to Windows 8. Or possibly later. (If memory serves, I think Microsoft has been hyping a database-driven filesystem since the initial discussion about "Windows NT".)
So while the data center guy in me is interested in 128bit Windows support, at a technical level, I'm just not hopeful we'll see it in 8 or 9.