what I'm longing for is a good G-code generator that is affordable, runs on my Linux or OSX, can generate toolpaths for milling as well as 3D printing and can work with files from Sketchup.

(Most makers I know don't use Windows and I think there is a huge opportunity for a polished product that will run on either Linux or OSX)

Slic3r is an interesting project that goes in that direction. Only for printing though. You can feed it an STL exported from sketchup and it will generate a toolpath. And of course it's all on github and completely free and opensource and multiplatform.

The major problem with it is that sketchup is a mesh editor, not a solid editor, so it sometimes exports geometrically impossible (non-manifold) objects.

FYI: sketchup doesn't support linux yet.

I know, but since I will be using either EMC2 on Linux or Grbl on an Arduino to run the G-code, I can live with CAM software that runs on Linux.

As would a 3d CNC router: scan with the scanner, print it roughly, then the router cuts it to high quality perfection.

It seems that movement hasn't been as rapid in hobby CNC machines as in 3D printers, probably because CNC machines are a lot more expensive. Good CNC usually requires two tool-tilt axes in addition to the standard X, Y, and Z - for a total of 5 axes, and everything has to be a lot stronger to apply enough pressure to the tool without warping. Hopefully once everyone has a 3D printer they'll use it to print some CNC parts and kick that movement into gear...

With that said, a 3D printer can be repurposed into a very weak 3-axis router pretty easily. Provided you move the tool head slowly enough and are cutting something very weak, they work okay.

The fundamental concept (having a computer move a tool head) is the same - 3D printers are just built out of weaker/smaller (and hence cheaper) parts.