I vacuum the vent of my ps2 once every 3 or 4 months or whenever I see there is too much dust on the ventiliation. When I first bought my ps2 last year, in the box there this notice or warning piece of paper that tell ps2 users to vacuum the vent regularly. I found and read the notice by luck. I never found any problem with my ps2 ever since I first bought it and I never have to clean the ps2 laser with the cleaning disk...
I think people should pay attention to the Attention paper that is in the ps2 box.