Twitter started as a way to keep in touch with your friends using SMS. You can see the vestigial signs of that because twitter has features that allow you to authorize each person who requests to follow you. Twitter’s main page when you login says “what are you doing?” reinforcing that orientation.
But at this point, twitter has clearly crossed over to be microblogging. The most interesting people to follow are not those who tweet that they just got on an airplane or are sitting down to lunch, but those who point you to interesting articles on the web or make a quick observation about the world.
Blogging has the same dichotomy. There are many personal blogs out there that talk about stuff only interesting to their friends, but the vast majority of blog readership goes to blogs that write about non-personal topics in much the same way as a newspaper columnist does.
Facebook too has a status update system, and it asks “what are you doing right now?” And for facebook, this has remained pure and true, because the people connected to you on facebook are your actual friends, or at least people with whom you have some personal connection.
This divergence makes things like the twitter app for facebook feel all wrong (it makes your tweets your facebook status). If you are using twitter to point people to news articles, talk about the world, inform about your business, etc, it feels way too commercial to have every tweet become your facebook status!
Twitter works well with search. It is interesting to search the whole twitter network on topics and to gauge sentiment, just as it is interesting and useful to search the blogosphere. Searching the facebook status update messages would be a gross invasion of privacy and frankly not all that interesting.
Personally, I find twitter a lot more interesting than facebook status messages, but they serve vastly different purposes.
It is interesting that both YouTube and twitter were started with the expectation that they would be primarily for personal permanent communication, and both emerged as outlets for citizen journalism. Following along the same lines, the next logical step for twitter is to promote the most interesting tweeters right to the home page (most followed? most highly rated?) so that the rest of the world, that may have no interest in participating as content creators, can enjoy the content more easily.