Tippet Size

I was out and about today and was speaking with a fellow fly fisherman and
he was discussing a local fishery where the fish were easily spooked. "I
always use a 7X tippet and I favor a size 16 Adams pattern." Without
thinking (I do that a lot), I responded, "With a 16 you would really want to
use a 4X tippet with that."

Well the discussion went on and it turns out that tippet has nothing to do
with the size of a fly (hook size to be precise and I guess a heavily
dressed fly would effect the choice of tippet as well?). Anyway, I always
used the rule of 4 on determining tippet size (size of fly divided by 4) --
I am gearing up to take on some smallies soon and will be using size 8 flies
so I be using a 2X leader/tippet. I didn't hold my position in the
discussion because I got to wondering if things have changed some with the
new leader materials etc.

So what is the thought on fly size to tippet size, anyway? If I am throwing
a size 4 popper would I use a 1X leader/tippet? Would using a furled or
poly leader allow me to select a smaller tippet than the previously
mentioned rule?

Chris