What the Alexander Technique has done for me is to act as a reminder to allow my back, and in my case especially my neck, to lengthen. It helps free up the joints from undue strain.
By practising the technique one learns to retrain the body quite naturally.
I describe the Alexander Technique, as a gentle series of positions that the body learns are the best ones for you. In many ways the learning is unconscious as it taps into your body's muscle memory and reminds me of the Chi work that underpins martial arts (perhaps this is a bit esoteric for some people). Through breath you relax and I enjoy my weekly sessions and they are a way for me to tune out of the rest of my life. In terms of posture, I am definitely more aware of my body position when walking and sitting, etc. and I am striding to embed this in all movements. It is slow but worthwhile and a good long-term way to improve posture. It also makes you realise that most of the furniture you come across is no good for you!