This is very solid advice. I aim for about $50/ hour before factoring product cost into anything I do, and have a couple of packages setup around that. For friends I throw a bit of a discount on top. Remember to factor the size of the vehicle, and I charge extra for cars that are dirtier than normal (I call it the mommy wagon tax).
Also having optional add-ons like glass sealant or pulling wheels to get the insides of everything better than you normally would are great money makers as well, and I hook friends up with those at no charge, time permitting.
Agreed. If I am doing full corrections I charge by the hour, especially on black paint. Otherwise if I am 1 stepping a car then I have a fixed price package.
The other thing I like to do for friends is offer them a discounted detail if they pay for a new product I want to try and let me test it on their car.