Well, the name is official, and it's been announced that it will be shown at PDC and WinHEC. At least according to Mike Nash, and he should know. From Mike's PressPass page:

As corporate vice president for Windows Product Management, Mike Nash heads the team responsible for market intelligence, pricing models, competitive strategy and incorporating Live services into the Microsoft Windows operating systems.

From the Windows Vista blog:

And, as you probably know, since we began development of the next version of the Windows client operating system we have been referring to it by a codename, "Windows 7."  But now is a good time to announce that we've decided to officially call the next version of Windows, "Windows 7."

"Windows 7"  I like it. Clean. Simple. Effective. Now, I'd better get back to making it great....