The internet is available to anyone with an internet connection. I know this seems obvious but the number of times that people have forgotten that continues to amaze me.
This means that:
If you write something about how trashed you were yesterday, people can read it. People like your parents (of particular concern if you are underage), your boss, your prospective boss, your friend who you told you were studying last night, and so on.
If you change your email address to reflect a major life change you have made, anyone who you email will notice. So, if I changed my email to firstname.lastname@example.org or email@example.com, then when you email people, they will suspect that you are tattooed or, you know, shacking up'.
If you change your profile - on your social networking site or your blog or wherever - to indicate a similar life event to the examples above, people will find out.
And just in case anyone is unclear, this is not how you make such announcements to family and close friends. Even an email is pushing it for those people, but that is certainly better than them finding out because your profile now mentions that you have three kids instead of none. Sure, we can argue that there are exceptions for estranged family and such, and possibly, depending on the circumstances, that might be true. But if you go ahead with this method of non-communication, you are likely causing further damage to that relationship. If you're okay with that, then go ahead.