I would tend to be suspicious of a pure 'software cnc' running under windows, at least until it had proven itself reliable.
However, I think a decent compromise is something akin to the Galil dedicated hardware solution for motion control. You don't have to buy Camsoft to create an interface, if you are the programming type, you can always get the developer kit and make your own interface. It might even be feasible to write a post to convert gcode to Galil commands.
Now bad programming of the windows/Galil interface can still cause problems whenever logic has not been created for every circumstance, but I think the dependability of the motion control itself is safe with a hardware solution running under Windows.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)