Just read this, thought it might be helpful, AFAIK it only works in 40/80 and probably 160GB PS3's, which is annoying for me....
Start off by turning the PS3 completely off from the switch at the back of the console and turning it back on while simultaneously holding the eject button.
A loud whir will signal your success as the PS3 console enters the self maintenance mode, with all of the internal fans instantly revving their little hearts outs and cleaning the innards of your PS3 from harmful dust particles - not to mention making a noise that we all thought the whisper quiet PS3 was absolutely incapable of.
After roughly ten seconds your PS3 will automatically go back into standby mode and you'll be the owner of a dust free console.