I am just lurking around on Twitter and Facebook (no user for both of them). Twitter works fine for me (e.g. when Peter King has written Monday Morning Quarterback the link is up on Twitter), but Facebook is very hard if you are not a user and want to know how a band sounds like. I've used Myspace for this before, but the new player and the fact, that most of the bands are nearly on Facebook exclusively, makes me use Facebook for this. Facebook really sucks for me.
If Mark Zuckerberg invented Twitter it would probably be Facebook, and Facebook would be Twitter.
Early Facebook was influenced heavily by Marks ideas and thought patterns, where he wanted to take a website, and it's "coolness" factor. It's not the name or the plan which makes the product, it's the people behind it, Facebook is Facebook because Mark Zuckerberg and the other early founders had tendencies towards certain design ideals and ideologies.
Facebook is for sharing everything, Twitter is for interests... Nothing does it better then Twitter's policy to limit a text to 160 chars... They don't need to work a lot on the front-end.. It works as it should work.
And it is result of their first version accepting SMS for input (SMS is limited to 140).