This thread has got me wondering just what it will take to destroy a box, so, in the name of science, I have removed one panel from an older P4 system (circa 2003ish), and will blow all smoke directly through the components (allowing the smoke to collect inside the case). I did briefly consider detaching the vent fans, however, that would throw off the experiment, as heat will certainly cause issues in short order.
I should note that this computer has been in my den since purchase in '03, and has been exposed to anywhere from 10-20 cigarettes per day for the last seven plus years, with no detrimental effects, other than a film of nicotine on the monitor, and lots of ashes hidden in the keyboard/mouse.