If you plan to upgrade your WinFX bits with the yesterday released January 2006 CTP of WinFX Runtime Components consider the following:
You do not need to do a fresh reinstall, even though that is what is suggested in the docs:
First, uninstall all December 2005 CTP bits in the following order:
Then, invert the installation process:
For now, I can't see any major differences in programming model of January <> December WinFX CTP.