I like the sentiments expressed in this blog entry by Dave Winer. Read the rest of the article. This is why I feel comfortable storing things that I write in sites as mentioned in the accompanying quote. In fact, this is also one of the main reasons that I find "Amplify" useful since it allows me to push content to all of these sites at the same time, thereby insuring some resiliency in my writing.
I also store images in flickr and in short what I'm doing is only using Facebook and Twitter for so called ephemeral content - text, pictures that I don't care if I lose.
If you put stuff in Facebook, it's even more silo'd than it is in Twitter.
However, if you put stuff in WordPress, even on wordpress.com, you have full fluidity. You are not silo'd. You can get data in and out using widely-supported APIs that are implemented by Drupal, Tumblr, Posterous, Movable Type, TypePad, etc etc. At least there's some compatibility. And in a pinch you could probably move your content to a static website and have it be useful.
