The idea of 'friends' was once very simple. If you knew someone, hung out with them regularly, and liked their company then they were a friend. While the people who still fit that description are still your friends, so are the people you have connected with on social networking sites apparently. Whether you talk to them, care about what they're up to, or have any interest in them whatsoever, they're still listed as friends.
This has muddied the waters considerably. I know several people who have thousands of friends on social networking sites. Do they really? Or do they in fact have a dozen real friends and hundreds of people they have met once and then added to their Facebook or Google+? I suspect future generations will be unable to distinguish between meaningful relationships and casual acquaintances.
Social networking sites bring out this side in many people, turning them into crashing bores who will detail what they ate for breakfast and the manner in which their body expelled it several hours later. Youngsters especially could become convinced that they are more important than anyone else, and that what they have to say should be read and responded to by a wider audience. There is also vaguebooking, which is a crime in its own right.
All social networking sites add to this information overload to a certain extent but Twitter is the main culprit. People are condensing everything down to 140 characters or less, so when it comes time to actually read anything longer than that, it takes a change of pace and a change of mindset to do so. I suspect you're even skim-reading this article. I'm not offended, we all do it, but it's another way in which social networking sites have had a negative impact on society.