Twitter integration was one of the rumored announcements leading up to WWDC, and Apple has delivered.
Users can associate a Twitter account in the iOS settings and other apps will automatically gain access to Twitter integration using the app, which means users no longer have to log in or manually add an account each time. Moreover, apps like Mail, Contacts, YouTube and Camera will all have extensive levels of Twitter integration.
Users will be able to send tweets directly from the Camera app or photo album (using Twitter's new native photo uploading features), as well as within the YouTube app. Additionally, users can grab photographs for their contacts if the person has an associated Twitter account.
The fact that this is built-in at an OS level also means that it will make things easier for developers who want to build deeper Twitter integration into their app experiences.