QUOTE(earplugs @ Aug 22 2007, 09:36 AM)

Anyway FWIW how I sit now is:-
Left buttock very near the front of the chair right buttock further back. My hips and torso are facing out at about 45 degrees to the right of where the chair is pointing. Because of a history of back problems I try to keep my whole torso from hips to shoulders straight with no twist and poised as if I was standing.
Left leg points directly forwards from the front of the chair, thigh parallel to floor, foot flat on floor, foot slightly behind the knee so angle at the knee is slightly less than a right angle.
Right foot is somewhat tucked under so it is slightly under the chair and roughly under my left buttock and on the toes of my right foot with heel off the floor. Right knee is low with right thigh sloping down.
Violin points a bit to the left of where my left leg is pointing.
For those with a short torso (compared to their legs), this is an ideal sitting position and one I also adopt, but I tend to have the habit of letting my right leg end up with the knee almost touching the floor.
If you are short in the body, ie. shoulders to hips, then the risk of hitting the bow on your right leg is quite high. For those with a long torso, it's less of a problem.
I agree that plastic chairs with raised edges are the most uncomfortable ever.
It's a case of adopting a postion that suits you and your physique best, but also one that doesn't interfere with other players if you are sharing a desk in an orchestra.