Twitter Support acknowledged the problems occurring yesterday.
We’ve been experiencing outages across Twitter and TweetDeck. You might have had trouble Tweeting, getting notifications, or viewing DMs. We’re currently working on a fix, and should be back to normal soon.
Some users were unable to log in to TweetDeck at all.
There has been no subsequent tweet confirming things are back to normal this morning, but reports of problems do seem to have died down.
However, many are finding that they needed to log in to TweetDeck again this morning, having been logged out during the outage.
On a more positive note, Twitter began rolling out Direct Message search to all iOS users yesterday.