So, you have made a post on a forum when you are a young man (or women), it may even be slightly embarassing. You might of got drunk and your friends have put a photo of you in an embarassing position or situation and you go for a job interview.
Your new employer, even though they cant formally use it, will do an internet search for your name. If you are clever, they will find a nice blog of you and your cat. Or they can use a people search engine such as Pipl and find all kinds of things.
Remember, dont post anything that you might be embarassed about in the future or have friends connected to you who might become a liability in the future.
Check it out for your own name and be scared.
You will notice, if you search for yourself that the information is currently seriously out of date (especially electrol register) and gets confused. But a worrying new public development.
The web never forgets.