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.