How far apart do you position your speakers ?

Hi Wolf, To answer the question:
"Doesn't the nearly infinite disparity between various speaker's responses in rooms, including tweeter off and on axis dispersion and woofer loading sort of obviate set-up formulae?"
I don't thinks so. At least as far as how your speaker loads or couples to your room. The idea is to be far enough from walls to avoid reflection and be close enough for proper bass reinforcement. Then to be in the right seating position to get the most from your soundstage.
I don't think that Whether you are 83%, 95% or triangle is any more important than understanding standing wave, reflections and reinforcement, this is where some type of formula could come into play. On or off axis listening is a factor of what your final frequency curve is in the room. As, I'm sure that you know, as you take your speakers off axis, you change the top end response heading down to your mid range. If your room caused some sort of peak, much of this could be alieviated when you go off axis, or if you have a very flat response, most of us would like to listen on axis.
Either way, the boundries, could be summed up mathmatically.

After reading all of the responses, I wanted to share my experience. I have a room that is 12 feet by 23 feet and i have the speakers on the short side of the room.The speakers come out 56 inches from the wall behind them and I have about 8 feet behind my listening chair. Because I only have 12 feet, I found that when I had the speakers spread to far apart, the sound suffered in terms of the most natural bass sound. I ended up settling for the speakers to be just over 6.5 feet apart with very little toe in. As I said, when i went any closer to the side walls, I did not like the sound of the bass. I sit 9.75 feet away from the speakers. This works well in my room. Every room is a bit different and you have to play around to get the best listening spot. Most rooms have issues but if you let your ears tell you what sounds right, you can usually get a good listening situation. You have to experiment and most of us have rooms that are less than perfect. Room treatments can help. Another factor is whether your spouse or you is comfortable having speakers come out in the room. As I stated mine come out 56 into the room, my dog Hanna does not object but not every spouse feels that way and there may have to be compromises.

Obviate: To anticipate and dispose of effectively; render unnecessary.

Now that we've cleared THAT up...Pettyfeveresk: I am concerned that your spouse is named "my dog Hanna"

My listening room has furniture, book cases, paintings, a glass wall, moose head (not really), a high sloping ceiling, and no formulaic solution. So I merely listen...combfilteringstandingwaves be damned! Also..."off axis" is extremely taste and speaker design driven and again, no formula, especially if you're face is over 6 feet away from the tweeter, and rooms generally do NOT have a specific "frequency curve" except what can maybe be measured in one spot, and that has zero to do with music (soundstage specifically) unless you listen with your face stuck to the window or you hang from the ceiling fan and measured those places. I've used a few vastly different speakers in that room...all requiring COMPLETELY different positioning to get to a sweet spot.

Here's my formula, try it if you get curious or bored:

Speakers 1/3 into the room
Chair against the back wall (make sure the wall behind you is not hard/bare)
Speakers spread 83% of the distance from your ear to the plane of the speakers directly in front of you
Toe in to taste, I suppose this will have a lot to do with speaker design

My room is 13' front to back, 12' side to side.
My speakers are a little over 4' into the room and are about 68" apart center of driver to center of driver.

I went to a shop in another city a while ago and the owner suggested the 1/3 into the room and chair against the back wall. It went against what I believed, but I got curious and bored at the same time so I tried it.
I got the 83% thing from this thread and it actually worked pretty darn well.
It may be that my room is small, a cube, or whatever but this is where I have my speakers.

Is it that the distance between the speakers is 83% of the distance from the speaker to ear or plane of the speakers in front of you to ear? There is a difference.