Much of coffee's flavour comes from a balance of acids and oils. These, particularly the oils, are sensitive to temperature. But unless you're drinking your coffee all day, you're unlikely to notice it. Real spoiling sets in after several hours at the kinds of heat you're probably running your Ember mug at. Most drip brewers with heating elements for the pot keep the temperature too high (often just below boiling). A steady heat is much better for the flavour than reheating. (This is what I remember from working at a coffee shop way, WAY back when I was at university.)
