I have heard of people getting killed from someone online, people getting stalked online and cyber bullied, being outed in real life from online, losing your job over what you do online like posting something on facebook, and people have used information against their ex what they post online. That happened with my friend on WP, his ex was taking all his posts he make and use them against him in court to manipulate the judge. All serious business.
As DW a Mom says, what you post online isn't private and it's there for life unless the forum gets deleted.
Ways to protect yourself:
Never post your first and last name
Make your facebook profile private and don't allow any co workers on your friends list nor your boss
Never tell people in real life your user names you go by online
Always use a different email address than you do in real life
Use a email address to register on forums, not the one you use in real life when you apply for jobs
Use a different user name for each forums/websites you go to (this prevents people spying on you)
Use a different email address for each forum you register on (this prevents people spying on you)
Never tell people your other user names you use at other places
Yep these are tips I came up with but I don't follow them all. I only follow two of them and that is posting your first and last name and saying what your usernames are online. I never do that.