I'm very interested in this subject as well, but my experiences are different than those who've posted thus far.
My room measures approximately 18'x25', but is attached to my foyer and it has a large opening to my dining room with 14' high cathedral ceiling. I have my speakers setup on the 25' wall and my seating position is right up against the opposing wall.
My speakers are about 12' apart and about 13.5' from my listening position. The speaker's baffles are 38" from the front wall (the rear of the speaker is 19" from the front wall). They are toed in to aim at a point about 5' behind my listening position.
I didn't use any particular technique to position my speakers. I first position them for aesthetics and move on from there. I wrestle with subwoofer placement more than anything, having it on the outside of the main speakers or on the inside of them (currently on the inside). This again is mostly for aesthetic reasons as the subwoofer performs very similarly in either position.
For my current speakers, and two previous pairs prior, I don't find that fine positioning them really changes things much. I use REW with a Behringer ECM8000 mic for all in-room measuring. Moving the speakers closer or farther away from the front wall affects mostly frequencies centered around 150Hz. Toe-in affects frequencies around 16kHz and up. In either case, I have been hard pressed to hear the differences. I don't think the changes centered around 150Hz are really audible, and the toe-in affects imaging so much, it hides any frequency response changes.
I've dabbled with room treatments behind my speakers, but the audible changes were just not there so they are gone. I couldn't really discern any change in sound whatsoever. However, I do think my room sounds very good without any treatments. I attribute most of this to the fact that my room and setup have minimal first reflections. On the left side is my brick fireplace that has some level of depth into the room and on the right is my front door about 15' away. There is also a pair of french doors that are on a 45 degree angled wall. The cathedral ceiling is also fairly steep and all these features combined are minimizing reflections to my listening position.
The one major issue I've found is that having my listening position tight to the rear wall is not good. While it's not all that bad, simply moving the listening position about 12" more off the rear wall really solidifies the imaging from the speakers. The sound is overall more airy and defined. It measures slightly different, but the change in sound is not coming from volume at particular frequencies, but more from the scrambled reflections of the rear wall (if this makes sense
). Nonetheless, I'm currently trying to figure out a way to move my couch 12" off the rear wall without it looking out of place...