fire at rideside.net
OK, just burnt dust. Looks like the fan fell off (actually, a couple of the tabs look melted) the CPU's heat sink. Dust caked in there on the fins, and the machine --luckily-- would only stay running a few minutes at a time. After inspecting the situation, I pulled out the vacuum cleaner and removed the offending material.
Now, it smells like late fall and the radiators are just getting warmed up. Or like someone left the iron on. Let's see how long this holds...