I've never had the rear wheel lift when braking heavily on the front, even before I started loading the back up.
Today it'd be virtually impossible for me to lift the rear wheel as there's about 20kg sitting over the rear axle, dynamic friction on the front wheel would take over before that happened.
I find I use the front brake more (obvious because I wear out the brake pads faster there) but I do use both. The set up here is typical for bicycles in this country: left=rear, right=front. I have an indicator light system for signalling turns, and only use hand signals when that is out of action.
Going downhill and doing a right turn for me is a near impossibility whilst signalling with hand signals, since I need my right hand to control my descent, a sufficiently steep downhill grade will prevent the rear brake from being effective even with the extra load.
A couple of times I've been forced to ride places with only a rear brake, basically in the days before I upgraded my commuter bike to hydraulic brakes, there seemed to be a fault with the brake that would eventually wear out the brake cable and cause it to fray about the same point. A few times I've ridden to the bike shop with a brake cable on the verge of snapping: those runs I had to remind myself "Don't use the front brake!" and noticed just how poor the rear brake alone performs.
That said, I have seen bikes equipped with a rear brake (a disc, no less), and no front brake. I've often wondered how they handle.