The endeavor that drove me, a passionate user for several years, off the site for good. It's sad that they watered themselves down to become a second-place Facebook.
Maybe it's not even their fault, and it's just a side effect of being a public company and being measured by growth instead of by the uniqueness and quality of the product. It's still sad.
When the dust settles, there will be lesson in the danger of engagement-metric based product design. Twitter has a "while you were away" feature that shows you their idea of the tweets they'd like you to see first. (Even if you return to the site 5 minutes after your last session.) (This is different from the non-chronological timeline, and doesn't get turned off when you disable that.)
When you dismiss it, it asks you if you'd like to see less of that. It's completely ambiguous and unexplained whether they're asking whether you disliked those specific tweets or the non-chronological aspect of the timeline. A lot of users have been vocal about hating the feature. By dismissing it are they actually burying certain friends down further on their timeline? Who knows? Some people are guessing correctly what the meaning is, but others aren't. They're feeding a certain amount of garbage input into their algorithms.