Interesting to read this since just last night I asked my (group) instructor to recommend if she could a "good" video from which to learn intermediate (American) ballroom. Her reply was basically non-comittal, but to watch tapes of good dancers, such as Dancesport competitions, and note the posture, technique.....
She, by the way, has just begun a new Beginner's class for Ballroom, and it is only $8 a fifty minute lesson. This class will go on forever, eventually getting to advanced beginner/intermediate level. I have no doubt she is an excellent dancer and teacher, having done both for about 15 years, (and I have seen her dance), but alas, I am a little impatient, especially since my partner and I are beyond the rank beginner level ("1 and 2, 3 and 4, pick it up, put it down" for Swing, as an example. While I eagerly await the class to reach a little higher level of instruction, I can be glad SHE doesn't get $75.00 an hour!!! So, there is some good to it.
So aside from thanks for the info from former participants, I would just like to add, you really can learn alot from just watching tapes of good dancers, or going to a dance and watching couples whose style you like. Especially if you just want to be a good/excellent social dancer.
(You may want to see if your local university or college has a branch of the ballroom dance association. Ours here in Madison Wis does (UWMBDA - affectionately known as You wahm da) and go to their dances. Those college dancers, here at least, are really fun to watch.)