I think it's ridiculous. I gave it a try, and realized it was just a "status update" engine, in my mind. Not at all this revolutionary cultural phenomenon its heralded to be, so I gave up fairly quickly.
News feeds and RSS and regular Googling and using one's eyes are for news and updates.
But that's only my opinion. I think it's some sort of drug, because my roommate apparently joined one half hour past. His message on his perfectly adequate facebook status feed?
"Crap! I joined twitter."
His use of the colloquial "crap" suggests that he dislikes this development, and considers it poopy.
Yet he joined. Clearly an addiction response, because it has no practical value. And he's already a clear, admitted, and hardcore facebook addict.