I suffered from the same problem mate then I came across this simple solution, actually from a Sony Technician in our workplace.
You need sawdust, that's right wood chippings. What you do is do not clean any excess dust, instead you do a thinly covered layer of sawdust in a tray and put your playstation in it. Very importantly, you have to stand it on it's side in the tray of sawdust WITH THE VENTILATION ON THE SIDE FACING DOWNWARDS, into the sawdust.
Switch on your playstation and leave it like this for 20 minutes only. Keep any eye on the PS3 throughout all of this time.
When you have finished make sure you turn the PS3 off, and remove the power from it, before using a hairdryer to remove any remaining dust or sawdust.
Hey presto! You'll never suffer from dust again. I haven't for about two years since doing this.
Let me know how you get on.