The person I asked about lunges says, let that rear knee just touch the ground. Does that ever work the supporting leg more! I can really feel how different it is.
It wouldn't surprise me if ten different coaches each gave somewhat different instructions for how to do a correct lunge. That seems to be the nature of physical training. On top of that, there seem to be a number of variations on the lunge. I suppose that's to keep things from getting too dull.
Whatever I've been doing, on bike and off, seems to be having an effect. On this morning's ride, I averaged just under 14.2 mph, for an hour (and one minute and forty seconds) of riding =)