My friend Andrew has been doing a lot of research lately to find more information on Rotor beyond the excellent Rotor book (Shared Source CLI Essentials). Yesterday, he posted a wiki link to a great architectural resource for Rotor: Software Architecture of 'Rotor' CLR.
I've said it before, and I will say it again, one of the BEST ways to learn what's going on under the CLR is look at Rotor code.