When I started with social network there was Orkut & Myspace there UI user interface was very difficult to understand first of all. The orkut had the worst interface everything just black and notification flashes in red .
Facebook has overcome all of it the user interface is as simple as a kid can use it . It has revolutionize the peoples life .i Being at home can know what my friends are watching, where have they been a day and many more things, .
When any one want to know about anybody he just first searches on Facebook. Thats the power of it and almost all the people are joining Facebook so all are connected as a ecosystem that to not only limited network but all over the globe .
Facebook now is running at its best with a simple interface have a chat with online friends and a trends that that informs you whats happening on globe whats trending.