(It's in Toronto, actually!)
So my point is that the notion of "subject" is not always applicable. It is probably derived from portraiture: landscape photography often does not have a subject in this sense (although it has one or more points of interest).
Cf. for instance the two photos in the lower left corner of Robert Teague's portfolio:
It would be hard for me to say what is the "subject" of the picture in the lower left corner: the lake? the mountains? or the dark portion of ground? Likewise, in the next picture, which is the main subject: the mountain in light or the mountain in the shadow? On the next photo, it's clearer to me that there is a main subject, the group of round boulders, and the effect is different.
My reading of Robert's photos (and I hope he will not mind my using him as a prop for my argument :) ) is that they work because of composition, and because all the varied elements hold each other together. I personally really like the light mountain/dark mountain picture, because it's a great example of balance: the salience of each element depends on the salience of the other element. Plus, the third mountain brings just a little bit of asymmetry in order to avoid monotony.
It's like the ukiyo-e of the wave before mount Fuji: negative space is as important as positive space.
So to make a long story short: the composition of your whole picture is important, as an organic whole, and positioning your main subject, when there is one, should be made with respect to the weight of other elements in the picture.
In the UK (and IIRC, Japan), they put the subject on the left, whereas in most of the rest of the world they put it on the right.
Wait, no, that's how they drive! :) :)
In general I agree with Michel HV, however, most of my images have a “subject” and the subject usually “faces” either right or left. I don’t photograph people, so the term faces is not literal, but unless the view is straight on, the composition usually leads the eye either right or left. If the subject faces left, I leave more room on the left. Of course this has something to do with what is actually to the subjects left but if the subject faces left and more space is on the right it is equivalent to a photo of a person walking out of the frame.
A good composition is one in which the elements of the composition are visually balanced. So (as Michel said) placement of the main subject has a lot to do with the “visual weight” of the other elements. It has nothing to do with whether the composer is right or left handed.
An object is neutral if its contribution to the impact of the image is of little or no importance. Sort of like something that’s there but we wouldn’t notice if it wasn’t or if something else were in its place. This could be the sky or grass or water etc.
A supporting cast object is something that enhances the image with its presence but the image could stand up if it wasn’t there.
The main subject is simple. It’s the one thing that “has” to be there. Without this element, the image has no compelling reason to exist.
I have a tremendous built in bias to the lower right corner. Not quite sure what it is, but I usually find myself drawn to placing important compositional elements there. It is very confusing learning to use a view camera, and I go crosseyed or get vertigo quite often. Aside from those effects, I find I am putting more subjects on the lower left because of my bias to the right combined with recognizing the top of the groundglass to be the bottom of the photo makes me locate a lot of subjects in the top-right on the groundglass.
I worked in a darkroom which was designed by a left-handed person and resulted in the dev tray being placed on the far right hand side. It's not a good idea to ask opinions from left-handed people! :)
This is a topic I always have a problem with. I am right-handed but left-eyed. I have composed images where the main subject is on the left side, knowing the rule about reading right to left. It feels comfortable for me, but also I compose the other way too. I guess as long as the subject doesn't look like it is leaving the photo on me, I compose both ways.
I also read magazines from back to front then front to back.
One last thing...I paint watercolors which puts me in my left brain.
I'm getting really confused now :)