Update: All of these functions are now back. Looks like Twitter was having some technical trouble.
A load of Twitter's functions just disappeared overnight. So far, we can't find any update from Twitter about why this has happened.
What we've found so far:
No more auto-complete suggestions in the search bar.
You used to get suggestions for account to follow when using the search bar. Not today.
No more auto-complete suggestions when writing Tweets.
Same weird behaviour with the compose Tweet box.
No more "Me" and broken "Connect" tab
To the right of the "Discover" button, the "Me" tab would glow when you had a Direct Message in your inbox.
The "Connect" page now only shows mentions, no retweets, favourites or follows.
No more photos and videos grid on profile pages
The photos and videos grid from the left hand side of profiles has upped and vanished.
No more "More" button, which used to let you embed and report tweets.
That button used to show to the right of the Reply, Retweet and Favorite buttons. After a prolonged campaign to have Twitter introduce an easier "Report Tweet" button, that's now inaccessible.
Tweetdeck allows you access to those "More" functions, so could be a decent replacement for now.
All of these functions were really useful, and they've disappeared without a word.
If you find any more missing functions, let me know.