I can know exactly what twitter is and still not want an account. I can get what I want out of twitter, and twitter can get access to my eyeballs by just showing me things when I want to see them.
Don't get me wrong. I loathe twitter, and I don't have an account. My point is that twitter doesn't need to do the hard sell on what it is anymore - as far as the public is concerned, it's almost a utility like power or water. It's everywhere, through everything, and it's "just assumed" that you use it, whether you actually do or not.
My point is that if people are online and looking at the twitter homepage, they know what twitter is already. The exceptions to the rule would be a vanishingly thin slice of netizens.
