I am certainly not a coffee expert, but from the decent amount I know about coffee and the large amount that I know about all-grain home brewing, this seems like the worst way to make coffee with the possible exception of throwing the grounds into a pot of boiling water.
The biggest issue is the high temperature- nearly boiling. That can lead to excessive extraction of tannins and a supremely bitter cup of joe. If you've ever left a tea bag steeping for way too long in your cup of hot water, you know what tannins taste like. Incidentally, if you are using boiling water in your french press you may be doing the same thing do a lesser extent. Letting the water cool for a few minutes (say to 190F?) will improve the flavor. So, with the percolator not only are you exposing the grounds to nearly boiling water, you're doing it over and over again as the coffee recycles.
Also, you're going to lose a lot of aroma compounds. When the percolator sits on your counter boiling and condensing your coffee over and over, it is essentially acting like a distillation column and is stripping those precious aromatics out of the coffee and into the headspace of the pot, then out they go.
Finally, the engineer/scientist in me hates the fact that the strength of the coffee you brew is a function of time. I suppose you could use a timer and do a series of experiments to optimize for your own personal taste, but that's a lot to keep track of, especially before you've had your morning coffee.
Some reasonable hypotheses, but not quite accurate, I'm afraid. No biggie, I'm here to help. :-)
Tannins aren't an issue with coffee the way they are with teas or homebrewing, and water that's just under boiling (198-204 degF) won't result in a bitter cup of coffee. It's not the temperature that determines coffee bitterness. It's the water to coffee ratio and the quality of the coffee to begin with. It's all about extraction.
If you use too little coffee (say 4 grams per 6oz cup, instead of, say, 11 grams), you will overextract and get bitter coffee. Similarly, if the coffee is stale, and the aromatics have been long gone, all that's left is the bitter crap.
Strength isn't really a function of time. For one, it depends on your definition of "strength". If you simply mean full of flavor, then each brewing method has its ideal extraction times (the same way each has an optimal grind fineness). At some point you will begin to overextract. That's not really "strength", it's just overextracted.
For most press or filter type brewers, 4 minutes is a good extraction time. It's what I use in my French press and Clever Coffee Dripper (a filter cone that doesn't drain until you place it on a cup). For the Moka Pot (which I really like) I try to keep it the same. Note: Moka pots do not make espresso. They make a terrific concentrated coffee, but it's unfortunately not real espresso.
I can't speak for a percolator. I've never used one, but I suspect it could make perfectly good coffee as long as you unplug it/turn it off at the appropriate time (so you don't get the scenario Schwartz described). And as long as you use good quality coffee to start with, of course.
Just today I placed my first Mustachian order for coffee. 20 lbs of green (unroasted) coffee at an average of $5.50/lb. I used to purchase in smaller quantities, but now buy in bulk to save money.
