My eggbot pen servo was very touch sensitive - that is to say that the servo jumped around at the slightest and I do mean _slightest_ touch of its control wires.
Turned out the problem was with the Tower servo connector...it was a _very_ loose fit on the three-pin header, but the header itself was firmly soldered in place. I've used plenty of servos, and know what the connectors should feel like. I cut off the Tower connector, and spliced in a servo extension, and - presto! A good fit, and no longer touch sensitive. Woot!
The servo was still sealed in its factory wrapping, I think, when I got the kit - so it must have come from the factory in that pitiful state.