I'm currently running no cats, and MILs (with no check engine light or codes). I've replaced both front O2s, but both my rear O2s look to be original to the car (170,000 miles).
The reason for my questioning is because bank 2s fuel trim levels (short & long term) are far higher than bank 1s, which are near perfect. Also if you let the car sit and idle at a stop light for a long time you will get a puff of smoke when you leave. Or if you idle around in a parking lot you will get some smoke as you're backing into a spot.