Wow - beautiful work. I love the tripod-like legs, and the way they curve under to support the base plate. Simple and elegant.
May I ask - what reasons made you choose servos rather than stepper motors?
I suspect that servos will never let you get quite the accuracy you want; different servos may accelerate and decelerate at subtly different rates, and there's a lot of slack/backlash in the internal gears which doesn't matter when you're just using a servo to get from angle A to angle B, but will make a big difference if you want the combined velocity from all three to be precise and repeatable. Plus the internal gearboxes have quite a bit of 'bounce' in them, which may be hard to engineer around.
Having said that, I dread to think what the code would look like for stepper motors - it's a big leap to go from smoothly ramping three PWM signals over time, to sending out between three and six streams of variably timed pulses where the timing itself is non-trivial to work out and needs to run smoothly.
(I managed to build a crude CNC mill out of bits and pieces, and I naively thought it would simple to get an Arduino to not just act as an interface, but actually be capable of doing simple jobs itself - draw/cut circles, that sort of thing. When I actually started to have a go, I found the code waaaay more complex than I could handle. One axis, accelerating and decelerating from A to B was simple enough, but add another axis into the mix and it gets much more complicated... I gave up and started using TurboCNC. Gave me an enormous amount of respect for the guy who wrote it - there's a lot of funky maths going on in there 
Cool remote control and display, too. Next step: ethernet shield and a webcam, so we can all have a go at writing our names with it? 