I don’t mean to be unhelpful, but it appears access to username has been removed from the API, as far as I can tell. Places where an app may have been using username, such as in the old share dialogs, can no longer do that when used with the 2.0 API. I think its also a way of preventing apps from having access to usable unique identifiers outside of the app scope – any user IDs you retrieve under 2.0 API are specific to your app alone.