Now that I have a working TinyG and enough of a platform for some basic tests, I've started to think more about the software side of things. I chose the TinyG because I liked the idea of making the device smarter - a lot of designs rely on software packages on a PC like Mach 3 to do all of the low-level pulse timing, interacting with the hardware and stepper controllers using parallel port breakout boards, etc. I'm sure it works well and is quite modular, but it doesn't take into account the huge advances in microcontrollers over the past decade or so. Since I have a background in computing and electronics as well as a fully stocked machine shop, I don't feel bad about trying something a little out of the norm.
The other reason I thought it would be nice to try TinyG is that, at some point, I want to convert my existing manual metal lathe to CNC. The spindle control capability that is being developed for TinyG looks like it could be useful.
So I pulled enough parts out of the scrap bin to build a fairly nice Ubuntu CNC computer, which I've connected to TinyG via USB. The PC and TinyG are currently sharing a beefy PC power supply, however I think I'm going to split those up once I find another junk supply. It seems to work just fine, but I don't know how the supply will behave with "high" current motor loads - if it introduces ripple, it might annoy the CPU which also uses the 12V supply.
For a toolchain, I'm thinking of using PyCAM and/or Skeinforge to generate G code, and Inkscape and FreeCAD to generate the appropriate STL or other files. I'm going to give the free software a good shot before I start looking at commercial packages, but things like CamBam are viable alternatives if the free stuff doesn't suit my needs.
Since there doesn't appear to be any really good software for talking to TinyG, handling status information and uploading G code, I might write something up. If you know of something, let me know in a comment. I saw someone who used the status info to graphically draw the tool path as output from TinyG, and that would be a great place to start - if I can find it again!