You can download the binaries here or via the NuGet package. The packages contain the WriteableBitmapEx binaries. As usual all samples and the source code can be found in the repository.
Since the last WinRT release preview version, a couple of bugs were fixed and a new FromStrean method was added which loads an image stream into a WriteableBitmap. The project was also updated for the Windows 8 RTM version. Please read this blog post for more details about the WinRT version.
