Haven't seen this mentioned anywhere, so I'm cross posting my post from the FIRST Forums:
Warning about Joystick Initialization
Short Version:
The kit joysticks center themselves when the Driver Station boots up. If you're leaning on the joystick when the DS boots, then they'll be off-center and your robot will try to run away.
I suspect it's because the axes are measured with an encoder, so there's no absolute zero position. And no trim tabs. At any rate, I figure everyone else might as well benefit from my excessive curiosity.