Feb CTP is out.  Rather than have a separate install, Cider is now integrated into the Visual Studio "Orcas" Development Tools for WinFX.  (Note the designer requires a full version of Visual Studio 2005.)

Tim and Karsten have posted a list of "breaking changes" between Jan and Feb CTPs (most notable is the Mapping PI - which *was* the way to effectively do a "using" statement in XAML - now it's a much cleaner one-line thing).  Rob has posted his tool which helps you automagically migrate to the new syntax.

Note, if you're using Expression, then read this first before upgrading... you may want to wait till March to get the matching Expression designer.