I love excellent coffee, and for an excellent coffee, I can be very happy with very little sweetening and lightening. However, it is a bit of work, and we're suckers for convenience, in our home, these days, so we do enjoy a moderately great coffee (from our Keurig), instead of an excellent coffee from our regular coffeemaker, but in that case, a small touch of light cream is necessary, and once that's in there, I find that the cream often trumps almost the entire difference between great coffee and excellent coffee.
Incidentally, a "cup" of coffee is generally considered between 5 1/4 ounces (a "small cup", perhaps) and 6 ounces (a "large cup" perhaps). A "mug" of coffee is bigger - often between 1 1/2 and 2 cups of coffee, so you'd expect to use about double the sweetening and lightening. In our "super-sized" world, we now have "large mugs", which are actually between double and triple the size of a "cup" of coffee, so it isn't remarkable to double or triple the sweetening and lightening, as compared to just a "cup".
Having said all that, I tend to use two teaspoon's worth of sweetening per cup, but as little as one teaspoon's worth for an excellent coffee. If I'm lightening with cream, I'll generally need less sweetening; if I'm lightening with skim milk, I'll generally need more sweetening.
We generally stay away from flavored, though I'm not really averse to it. It's a nice change of pace sometimes, but I think if it was the general case, we'd get bored of it quickly.