Facebook

Facebook has reshaped social sciences around the world. Before such platforms as facebook and myspace, you had to get to know people.. by actually getting to know them.
Now if you ever meet someone interesting all you have to do is type their name in a box and a whole web-page pops up with their information, pictures, and list of contacts. There are privacy settings but as a whole they mean very little. 
You will never know who's browsed your page or what opinion they've taken of you from it. I find this disconcerting and personally have 'deleted' my profile for this reason. I found out when deleting my account that Facebook aren't so eager to let you go. 
In fact, you can't actually immediately delete your account. Upon selecting account termination you are given two weeks grace to 'change your mind'. This will often lead to automatically signing back into your account by accident and completely resetting the two-week deletion period. 

Even after the account deletion. Facebook has the right (you accepted when you signed up), to  "store data for as long as it is necessary to provide products and services to you and others". 

This basically means that Facebook have the legal right to hold any information you have given for as long as they deem "necessary". This allows them to hold the information for as long as they want until they're legally obliged to delete it after 5/6 years. 
This, considering the number of facebook users in the world, is a very dark omen for humanity.