When I was a therapist I went to see my account. One of my clients worked there and I said, without thinking: "Hello, how are you?" This was in the nature of a polite, general enquiry that I would say to anyone I knew, and not a specific client-based question. Later that day she phoned me up very angry and asked me why I'd asked her this question in front of her work colleagues who did not know she was seeing me.
I was very taken aback, but it taught me a valuable lesson about how careful you have to be in the field of confidentiality.
This was all brought back to mind because I've just published an article by Colleeen E Swan on the topic of confidentiality in counselling. She describes some legal cases which just show how complex this issue is.