downloaded and ran the new 6.0 version of reflector
http://reflector.red-gate.com/
it went ahead and installed its VS addin when I ran it:
It installed the *.addin files to both my 2008 and 2010 dirs.
In my already-running 2010 RC, the new menu shows up (no restart or any other user action required 
Nice!
This is one of the things I missed from my Eclipse days (now ~7 years ago), having a (then Java) decompiler in the IDE to step into third-party libraries to debug what’s going on.
