Thank you all very much, those were right on answers.

In short, Noise always happens, CPU's can respond to that noise in
unpredicatable manners, hence CPU run away *IS* a real problem.
Next, How important is that problem, Jay has gone into depth on
how to resolve it's importance. Thank you Jay.

In my experience, Logic boards do strange things when someone
nearby uses their Walkie Talkie. Also, in a networked system,
strange things happen when panels are interwired between buildings.
There are a lot of people that do not know proper grounding techniques
nor how or when to issolate segements of a networked system.

Jay, As you may know from other posting, I do work in security.
Regarding million dollar paintings... well, we have lawyers and
contracts to protect us against such losses, even when it is our
equipment that fails! Much like any standard software licence.

Kelvin, thanks for the thought, I like using external watch dogs
over the internal ones. My original question wasn't about how to impliement
but on the importance of implementing watch dogs.
But... since we're on the topic.... I'd love to hear how other people
"Kick" their watch dogs.

What I do to kick my dog...
Usually in the main loop of the program, I set a flag to allow a kick to
the dog. In a timer ISR, I check that flag, and if set, then I actually kick
the dog and reset flag.

****** NOTE ******
No dogs were actually hurt during this process.

Josh.