I think it's obvious when people are trying to shove their opinion on you as opposed to forgetting to pre-qualify their advice with the usual 'this may or may not work for you' line. That's why I really really appreciate the 3FC support policy where it says we can agree to disagree. Before I came here I was on another forum where members would gang up on each other if they disagreed with someone's weight loss plan etc. (you can tell which group I was in right?

). I was following medical advice from two doctors and yet these people would berate me about my calorie intake, with them all thanking each other's posts as if to give weight to their opinion that they were right and I was very much wrong.
Generally I take advice online as just that, advice. Nothing is written in stone and we know our own bodies better than most. It's really great to have somewhere to come and share experiences/fears and not be judged or dismissed.