I seem to recall reading somewhere that the late Duke didn't actually wear a Windsor knot but I don't expect that this is entirely true: it is much more likely that the real answer is that he wore different knots with different shirts and ties depending on the cut and material.

I personally don't really wear a Windsor knot and confess that I do view it as being slightly "racy" but it is also partly because none of my shirts have a wide cut away collar and partly because the even appearance of the knot itself doesn't add enough visual interest for me... however it is purely my opinion on what looks good on me with my ties and shirts (others probably have an entirely different opinion!) and I do see other people wearing a Windsor knot and think it looks good on them with their ties and shirts.

Interestingly there was a post on the late Duke's ties recently on:

http://asuitablewardrobe.dynend.com/

Scroll down to "on red ties knotted imperfectly"

I find, with some amusement, (it is always interesting to view how your own culture is perceived by others) that non-British commentators knock British Style on the head when they say it is the art of being well but imperfectly dressed.

It is something that many Brits seem to know intrinsically (bottom waistcoat undone, tattershall check with regimental stripes, mismatched tweed, chalk stripe with brown brogues, pocket handkerchief which matches neither tie nor shirt nor jacket, garters not matching tartan etc and so forth) and something which Jock Scot and others describe when handing out gems of advice.

In short I wouldn't worry very much about having the right tie knot; work towards the easy elegance of being slightly imperfect!