Oh how the excitement of keeping tabs on technology thrills us. To quote S. "Soma" Somasegar, Microsoft's Corporate Vice President of the Developer Division:
"The .NET Framework has always been at the core of WinFX, but the WinFX brand didn't convey this. ... With this in mind we have decided to rename WinFX to the .NET Framework 3.0."
Microsoft has indicated that the change won't affect delivery schedules of either Windows Vista or the .NET Framework 3.0 itself. More info.