The tipping point for Twitter will come when its need to be a public company surpasses what made it successful. Hello, new interface.

[youtube http://www.youtube.com/watch?v=wke0mT7IbrQ&w=600&h=315]

Twitter turned eight last week, which prompted a rush of business/tech journalism on where it's been and where it's going. (This happened a few months back, when Facebook turned 10. Would third-grade human version of Twitter be friends with fifth-grade human version of Facebook? Probably no…