In normal life—well, depends on whether you think California is normal, I suppose—I use feet, inches, pounds and ounces. For instance, I have no idea what I weigh in kilograms or how tall I am in meters.
But from the very beginning, all of my products were designed solely in metric. Millimeters are a friendly scale for small products, and decimal math is just easier to work with in general.
I've gotten to where time-keeping and latitude/longitude have begun to bug me, too. I wish we used decimal math for those, too.
Internally, AltimeterThree stores time and GPS coordinates as simple integers, which are just as accurate and more compact than the normal minute/second or even floating point degree representation. I vote we put 32 bits each on latitude and longitude, and call it a day. That's 1 cm at worst precision at the equator, which should be fine.