The WinFX February CTP is coming together and should be available pretty soon. For devs interested in Windows Forms / WPF interop, there's a new gotcha to watch for.
In the Feb. CTP, the WindowsFormsIntegration.dll is installed by the Visual Studio 2005 Extensions for WinFX (formerly known as "Fidalgo"). The default location for WindowsFormsIntegration.dll is C:\Program Files\Microsoft Visual Studio 8\Common7\IDE\Cider\WindowsFormsIntegration.dll. Use this path when you reference the assembly in your projects.
For historical reasons, the WindowsFormsIntegration.dll is also installed by the Windows SDK to the default folder C:\Program Files\Reference Assemblies\Microsoft\WPF\v3.0\. Do not use this version of the assembly, because it is incompatible with the current versions of WPF.
If you have projects built against earlier revs, you'll need to update the path to WindowsFormsIntegration.dll. I have updated all the samples in the Migration and Interoperability node of the WPF doc set, so if you have doubts, check those out first.
See Mike Henderlight's post for details.