Yes you should be careful what you do online. I doubt anyone is unaware that their boss may see what they post.
What I don't think anyone expects, is a national newspaper deciding to pillory you for no discernible reason.
If you are famous or in some way important, I can see the "value" in reporting what you say to the nation. If you are also being particularly hypocritical, I can understand why a paper would choose to expose that.
If you're just a normal person, talking about your normal life, I do think it's an invasion of privacy for a newspaper to circulate your thoughts and provide highly critical comment to millions of readers.
From what I understand (which isn't a lot) the PCC only provides a limited variety of complaints. I don't think invasion of privacy is the strongest argument - but if that's all the PCC will talk about, what choice do you have?
Thanks for your comment.