I just updated the WinRT XAML Toolkit for Windows 8 Release Preview. Grab the source code if you find it useful. Some things work better (ring/pie slice controls don’t flicker and shake any more). The CascadingTextBlock seems to have hit a new bug with PlaneProjections so you might need to set UseRotation to false, look/wait for a workaround or wait for a fix from Microsoft.
WinRT XAML Toolkit Updated for Windows 8 Release Preview