Here is an alert to all of you who are audiophiles who incorporate aftermarket power amplifiers in your sound system. For the serious enthusiast you know the importance of a "clean" install. No visible wiring etc. In some cases it may be the choice of the installer to run the amp's power wire THROUGH the ECU's protective box (right past the ECU either under it or otherwise) and follow the harness through the fire-wall. This is very obvious option because there is no need to drill a new hole in the fire wall and the wiring is completely hidden. However, depending on the wattage you are pulling, The EMF(i) 
Electro Magnetic Frequency interference COULD effect the cars performance. Especially in a situation where a performance chip may have been added.

Within the ECU is the knock sensor control. In some cases, where there is a large enough draw from the power amplifier, a small amount of EMF may bleed through the
wiring and cause a "fault" in the knock sensor system. This will automatically put the car into a "fault mode" and consequently retard the ignition timing, resulting in a loss of power. This loss of power may or may not be noticeable and this entire scenario does not necessarily apply in all cases. However in my particular case, when I had installed
and aftermarket performance chip and noticed a less than expected performance gain, I called the chips manufacturer and together we deduced that the EMFi was the culprit. 
Upon re-routing the wiring I was "blessed" with a whole new car. The power, torque, and acceleration came to life with a vengeance. 

So if you have and aftermarket stereo installed in your car, and notice an unexplained loss of power for no particular reason, check your amplifiers wiring and trace it. If it
goes through the ECU's box, re-route it and see if that helps.

Now again, this may not be the case with all cars, but I wanted to post this for all to read and to take under advisement....

Additonal information from Michael Michon (Mar-2001):

A way to avoid rerouting your power cable away from the ECU is to "artificially" shield your cable. You can do so tightly applying aluminum foil around the cable and taping together the segments of foil. At both ends, make sure your this shielding is connected to ground by connecting a small wire to a grounded nut. I routed the newly shielded cable underneath the clips that hold the ECU in place, which were also grounded, and this solved all of my interference problems with the APR chip!