Things twitter broke in the new design:
- When viewing a conversation, can't easily view further back in history (you used to be able to click on a tweet back in the history and see further back; now that just shows 'details' and you have to click on that, opening a new tab or losing current state, and view history there).
- When looking at people retweeting/favoriting you on the @Connect tab, you can't click through to see the actual tweet they're retweeting/favoriting (for example to check the counts on it). You have to dig it up in your timeline.
- When looking at the details on a tweet and seeing the retweet/favorites, you can't tell who retweeted and who favorited (this is sometimes interesting when looking at other people's tweets)
- The actions on each tweet which only appear when you hover over it can appear over the user's name. But the user's name is clickable to open a window about the user. So you can try to click the user's name and accidentally click 'reply'.
- Promoted tweets in the timeline are still dismissible, but the Dismiss choice only appears when you hover over the tweet, so it takes longer to dismiss (hover to locate the Dismiss choice, then click it).
- When you block someone, the blocked tweets stay visible; the block doesn't take effect until you refresh the page, which twitter avoids doing most of the time using AJAX. You can switch back and forth multiple times between Home and @Connect and the tweets remain. (This might have been true before, but it was jarring to me in a way that suggests it was a new experience for me. But I'm not 100% sure.)
Probably more that I'm forgetting.