If you have an air purifier it might help to stick it by the computer (or the room where you comp's in)... less likely of getting [as much] dust in that case. Also, there's other ways to keep dust out (homemade solutions; or some fans come with their own filters, but aren't fool-proof)
In my case, my dad smokes, but my computer is in my room (I try to keep the door shut... but you know - they say tobacco smoke travels through walls)
I don't leave that computer on often enough to have adverse effects on the insides, though (if it were outside my room it probably would be caked in 2nd hand smoke residue)... Case in point: smoking is also bad for your electronics too.
Too bad, though - I don't have an air purifier in my room yet
