sej: I'm always glad to see people interested in Fresco :-).
You said: I'm quite sure that Fresco (and its renderers) have to rely on an intermediate pixmaps for that as well. And as long as the pixmaps are local to one process (or in shared memory), "grabbing" them is as simple as reading local memory
Actually, no. There's no "grabbing of intermediate pixmaps". Everything is composited in the DrawingKits, and if you're using the openGL DK this can happen on your graphics hardware.
sej: I agree with you on the general coolness of Fink. Being a debian user myself, I wish it would resemble it more, but I understand it's not always a very good fit with MacOS X. It definately makes my life easier though.