It might be more likely that your cat is just no longer doing it's job. You saw from that site you listed that the front sensor should fluctuate fairly quickly between 0-1V (actually more like .2ish-.8ish) DC and the rear should have a pretty steady and consistent reading of .5V DC. This can be pretty easily checked with a voltmeter/multimeter, but you'd need a wiring diagram to tell which wires to backprobe at the o2 sensor connectors. Two will have to do with the heater circuit and the other 2 will have to do with the signal the PCM is looking at.
I think this would be best way for the average guy to look at what the o2 sensors are doing. There're probably youtube videos that'd show you how to do this.