We are working with the "Firmata" Arduino Firmware and PD / PureData.
Controlling a standard servo motor with it through PureData, the motor gets hot after, say 1 minute - however, it works fine when we are controlling it via usual PWM from "direct Arduino. Is that a common problem?
We also found that it "overdrives" to a certain point (and does hardly move back from there, we have to send varying (!) lower values to "lure" it back) - maybe this helps us...
The hardware PWMs that are built into the Arduino won't work for servos. You need to use very slow PWMs for servos. Also, many servos now just take pulses rather than a PWM signal. Using the fast hardware PWMs in the Arduino is probably causing your servos to heat up.
We plan on adding software PWM so that you can control servos using firmata/pduino, but its not in there yet. Any volunteers? For now, you should find some Arduino code for servos and use that.