I cleaned up a PC like that once, except the brilliant smoker in question had attempted to revitalize the HDD by injecting some new oil into it with a hypodermic needle. At least he used quality Pennzoil 30 weight.
I actually was looking at a bunch of old computers of a friend of the families because they only had one functioning one. (He liked linux over windows, and by the time I was done, he had like 4 working ones) That guy's kid had one that had a optical bay and all the PCI slots open. I even found LEAVES in that thing.
I was once called to a friend's home from work. He said his wife had complained that the computer really smelled hot. As I walked in the door, the computer suddenly started spouting flames from the PSU. When we opened it up (a bit later), there was so much dust that it was hanging like stalagmites (or stalagtites..whatever). The entire computer had filled with soot from the internal fire.