I did spend the best part of a decade writing blogs, because they felt like genuine finger-exercises in writing. I also did the NaNoWriMo challenge five times, just to see if I could generate long fictional content.
The distraction of Facebook is that it becomes a conversation, so rather than capturing permanent words, it more closely resembles idly sitting around talking in a Paris cafe, rather than being back in the garret, actually writing words down.
And micro-blogging seems even less relevant - lying around, generating sound-bytes or witticisms (like Oscar Wilde before going down to his cafe).
Dudley Moore: I'm writing a book.