Twitter is an information-streaming application that is used by people in all walks of life. It functions, sometimes in roundabout ways, as an instant messenger, email client, alert system, and social networking connectivity tool. It also offers fantastic, powerful searching and heavily encourages all-in-all openness.
Facebook, when I was introduced to it, was an application that allowed users to create a simple page with information about themselves, and connected them with people they knew in real life. Users could send messages to one another, both privately and publicly, post links, and upload an unlimited number of photos. Or at least it was.
Recently, Facebook revamped their interface and introduced a reinforced concept of status updates being a "life-stream" rather than a "summary of my week". Much emphasis is placed on what is going on right now, not what happened yesterday. This is great in my opinion – however, it totally changes what Facebook is for me. Prior to the change, when adding a friend, much emphasis was placed on adding relationship details for all of your friends. If you didn't know someone, Facebook wouldn't even allow you to keep them as a friend. Now, Facebook auto-suggest people that it thinks you might know, and encourages the meeting of people through Facebook itself. Nothing wrong with that of course... I'm just showing how it has been changed.
There's a fundamental difference here: Twitter changes with its users.
It changes according to the trends of it's users. Twitter does absolutely nothing to influence they way its users use its services. In fact, it evolves with them. For example, Twitter allowed users to view when people @replied to their tweets by going to the @replies section of the user interface. In this section, you could see a list of all the latest tweets that started with '@yourtwittername' and see what people had to say to you. After a while, users started adding @replies everywhere in tweets, not just the beginning. So, twitter changed the algorithm, and now you can see when '@yourtwittername' is mentioned anywhere in a tweet. Genius.
Facebook tries to change its users.
When was the last time you heard a bunch of Twitter users complain about a newly implimented feature? and when was the last time you heard a Facebook user complain of a new feature or interface change?
Yes, they complain constantly.
So, what is Facebook's purpose? To deliver useful content and introduce you to new people (while delivering ads), or providing a nice platform for friends to connect with eachother? If you ask me, Facebook's intended purpose is becoming less and less clear the longer that I use it.