We recently got in a Mac Pro from a client as a trade in against a new machine as theirs was faulty. The reason for its demise was a power supply failure - and when we noticed the yellowy tinge to the normally shiny silver exterior, we knew immediately why.
I've uploaded pictures full size (clicky!) this time so you can see the extent of the cigarette smoke damage, along with normal dust.
Cigarette smoke leads to dust clumps that stick together and block the air flow, leading to overheating and inevitably: failure. Normally dust will build up but not to a level where it causes failures.
|Optical drive enclosure|
|Air intake for the cooling of the PSU. The dust was so sticky and heavy we had to use a screwdriver to remove it - the henry hoover would not suck it up.|
|Sticky tar/smoke residue on the outside of the casing!|
|Cables clagged with dust and tar|
And it also begs the question - if cigarette smoke does this to a computer - imagine what it does to warm, moist, living organs in your body......