DMs can now be longer than 140 characters:
If you’ve checked your Direct Messages today, you may have noticed that something’s missing: the limitation of 140 characters. You can now chat on (and on) in a single Direct Message, and likely still have some characters left over.
I hope that abysmal DM user experience, when you have to click a button and enter a message in a modal window, will be improved. I will take this as a promise:
We’ll begin rolling out this change today across our Android and iOS apps, on twitter.com, TweetDeck, and Twitter for Mac.
Will be interesting to see if 3rd-party apps would be updated sooner than Twitter's official clients.