Fire

A couple months back, I was up at 1:00 AM in the morning watching TV. All of a sudden I could smell smoke. I look around and the smoke is pouring from the computer case. I never did see flames but I did pull the power cord as soon as I saw this. Is this normal for PSU's to burn up for no reason. Yes...I do leave my computer on overnight. Please don't tell me that I should shut my computer off every night to overt this. It shouldn't happen in the first place. I suspect that it was a build up of dust. Any thoughts?

Dust could be the culprit (that would require a lot of dust I would think), or perhaps a wire or something went bad.
Just remember to replace the PSU before turning the PC back on if it happens again.

It's usually the barebones, generic, or cheap psu's with low budget components that go up in smoke. You would be better off purchasing a high quality psu with heavy duty components. Some of the better quality brands that have an excellent reputation for high quality, reliability, and stability are Corsair, PC Power & Cooling, and Seasonic. For low wattage psu's the Antec Earthwatts series of psu's are good.

Not now.