What is your Stretching Philosophy

What is your philosophy on stretching?

I was trained as a Personal Trainer whilst living in Vancouver, Canada, we were taught all the different stretching techniques (dynamic, PNF, Static, etc) and many different stretching exercises. I have since enhanced my learning through books and further courses.
Whilst on my Personal Training course we were advised to dynamic stretch at the beginning of a workout, during and as part of the warm up, then workout, followed by stretching only the tight muscles and muscle groups, and not the opposing muscle. The theory being this would add balance, help correct posture and control to the muscle and tendons.
However a number of courses I have been on advise stretching all muscles worked whether it is tight or not, as this will flush out lactic acid and aid in the recovery of the muscle.
I have adopted an approach that focuses on the tight muscles relevant to posture and correction of, as well as including full body stretches, lower back and the obvious tight muscles identified during the client assessment, which we do as developmental stretches.
There is also the debate on how long you should hold a stretch for to show real improvements, I advise my clients to hold for 20 - 30seconds, however I have read reports that say 1 minute and they should be done twice a day to see any measurable improvements and benefits.
What are you thoughts and ideas?
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