I was trying to find an article about this very topic on Penelope Trunk's blog (I'm still looking and that's a post for later--WAIT, here it is) but came across this blog post of hers about social media identity instead:
Because mashing our social media together for the purpose of marketing one feed to another dilutes the value of social media. If you express yourself in the same way on a blog and on Twitter, then you don't need both.(Emphasis mine). I cannot agree with this point more. I used to always complain with my friends would write a LJ entry and then post the exact same thing on their MySpace. They'd get mad and say they could do what they want, but they were missing the point. Why would you just repost the exact same thing, when you have 2 audiences with the potential to write twice as much? I'm just going to stop reading one site or the other if you post the exact same stuff. This is why I will not follow any Twitterers that simply post links to a blog, or add a company on Facebook that just says the same stuff I can find on their homepage.
Each of us is multi-faceted. With a selection of media to choose from, we can express different parts of ourselves in different ways.