Dynamic translation would be rad.

It's true that @Noah never got enough credit for his early role at Twitter. Also, he came up with the name, which was brilliant.

A nice (and easy) touch would be to offer to import the user's Twitter avatar during the sign up process.

Twitter: "We're introducing our own version of TwitPic." TwitPic: "OH YEAH? WELL WE ARE MAKING OUR OWN TWITTER."