Im not too sure about the betraying their trust thing for offering advice but I do know that I have personally found people 'offering advice' on SR uncomfortable sometimes. As I have said previously, no one knows the true nature of your circumstances or relationship to be able to say 'leave' when you are not ready to or dont want to. I much prefer the SH&E philisophy from contributors on SR. I read what I want, take what I want and make a descision that I am comfortable with for my particular circumstances.
I love the no cross talk when someone is speaking at Al-anon. It taught me a valuable lesson in just listenening and not jumping in which I had been prone to do before. This has also helped me with detachment when AH is ranting about something I dont agree with.
At my Al-anon group we always stop for a drink and chat after the meeting and this is the time when feedback is offered although at my group we are very carefull not to advise. I like SR for perspective, views, opinions and experience and like the balance that both Al-anon and SR offers.