When talking about the factory water to oil heat exchanger, it's helpfull to look at the bigger picture.
Weather/geographical conditions, cooling system layout, and cooling system loading are all things that need to be considered when designing an efficient oil cooler system for your particular set-up.
The factory antifreeze to oil heat exchanger works very well for many people.
I monitor the oil temperature in all my engines, and using the factory water/oil heat exchanger it's a rare day I've seen the oil temp outside the goldilocks zone. (Warm enough to keep condensate from forming/cool enough that it's lubricating/flow characteristics are optimal)
For those that live in areas where you'll see four seasons, the factory heat exchanger set-up is hard to beat.
That said, it's not the best choice for everybody.
The heat "exchanged" at the water to oil heat exchanger has to go somewhere.
In the case of the factory set-up, it's into the coolant, and that raises the thermal loading on the system.
For those running a civic or other smaller radiator set-up, that can start to push the limits of the system. This is especially true for those that live in the desert/southern states.
Whatever choice you make, an oil temperature gauge will go a long way to alerting you to a problem in the system. /ubbthreads/images/graemlins/wink.gif
Combined with an oil pressure gauge and a voltmeter, they make up a nice engine monitoring package.