I wanted to raise a scenario that I think could be handled better by Twitter’s API.
If you send a tweet that is intended to be a reply, and post the status being replied to, and the tweet starts with a @username that doesn’t exist, then I don’t think this tweet should be distributed to all of the tweeter’s followers.
Usually a mention to another user is only distributed to mutual followers of the two users. Savvy tweeters with a lot of followers are likely aware of this. Circumstances can lead to someone reply’ing to a user and intending it to only go to the recipient. However, if the recipient’s name has changed before the tweet is sent, then the tweet will go public. This can have detrimental effects.
As a couple of possible solutions, a) the tweet could be acknowledged with a 200, but not distributed beyond the user’s own timeline. Or b), the API could raise an error (404 maybe?) - if an ‘in reply to ID’ is set, and the username at the start of the tweet doesn’t map to an active user.