It works a treat! On the whole I'm noticing about 8°C to 9°C drops in operating temperatures.
Of course I'm aware that it's subjective, but my SMCfancontrol reports:
34°C at 2,500rpm (idle)
45°C at 2,500rpm (running Photoshop CS3)
So I'm convinced that it does help with cooling.
On the downside, it does get a little noisy. I suspect that it has something to do with my table surfacing resonating. It IS whisper quiet on a glass work top.