The team foundation extensibility kit is available as of today! This goes with the December CTP release and includes quite a few things. For those of you following the work item extensibility it includes updated specs and updated witimport.exe for creating and modifying your work item types. There is also early documentation on the work item API/object model. Enjoy.
http://download.microsoft.com/download/5/4/6/5466ad0d-dd6d-4b2e-9402-63352bda1798/VSTF 1204 CTP Extensibility Kit.msi