I think you're right about usage patterns. For example, I know many teens and college students use protected Twitter accounts for communication (private, follow 25 people, 25 followers). It definitely varies by region, and even friend group.
I'm curious why you disagree about the opportunity for Twitter though? Do you think the brand is too strong, in a limiting way?
What about Facebook? Do you agree that their brand is irreversibly poor? What about the email opportunity?
Looking forward to discussing, and feel free to add anyone else that you think might have an interesting perspective.