Buzz,
I don't know how many times this question has been asked, but each time it is I find that I do not know of an answer for it.
I shoot very few clays, though some forty odd years ago I shot 20 or so rounds of trap ever week on the two nights our trap club met.  I do hunt pheasants and prairie grouse 110 days or more each year.
I have no answer because I am completely unaware of any leading.  I just look at the bird and shoot him when the gun butt reaches my shoulder.  
I know I must lead them and suspect that I do so as part of the gun mount, but I honestly am so totally unaware of lead that if I should think about doing so, I miss miserably.  And I miss nearly always if I don't take the bird as the gun mount is completed, especially if the bird gets up underfoot and I have to wait on him.
I would bet that I am not alone with this.