Are Tweets Copyrighted ?

Here is a question for all you legal scholars out there.  Is a tweet copyrightable ?  Is a tweet copyrighted by default when its published ? Can there possibly be a fair use exception for something that is only 140 characters or less ?

I got to thinking about this when I tweeted about an NBA game.  I tweeted to the people who follow me.  While I never asked that they not distribute it to other tweeters,  i did not give anyone permission to republish my tweets in a commercial newspaper, magazine or website.

So when an ESPN.com or any other outlet republishes a tweet, have they violated copyright law ?

Is twittering the process of publishing in 140 characters or less, or is it a private communications to those that follow you ? Even if you dont block outsiders from seeing it ?

You could also extend this to Facebook. Do you own your status update ? Is it a private communications between you and friends, or is a published work ? If a newspaper or website wants to publish your status update, do they need permission first ?