I had this light come on (on my 02 Focus SVT) a while ago, but it wasnt while driving. i was running diagnostics on the car with a Snap-on "brick" scanner (graphing-capable ODB II scanner) and the process was interrupted. which seems to have caused the same light to turn on. That was the only time i ever saw it on, and after resetting the computer it hasnt happened again.
is this useful information? were you actually DRIVING when it turned on?
has it come on again since?