This post reflects the opinions of the author and not necessarily those of Mashable as a publication.
Twitter CEO Dick Costolo has 99 problems, and revenue growth ain't one. The company announced income of nearly $243 million for the previous quarter Wednesday, beating analyst estimates by more than $20 million. It's on track to make a healthy billion dollars and change this year. Its advertising strategy is bearing fruit. If that were all, Twitter investors would be doing a victory lap right now.
Instead, they're heading for the exits, driving Twitter shares down a little over 20% in after-market trading. Why? It's not that people are leaving the service; the number of Twitter users grew in the fourth quarter. No, Twitter's own stats reveal the real trouble with a very fundamental kind of user engagement.
See also: Twitter User Growth Slows in Q4, Stock Plummets 18%
Admittedly, user growth was disappointing — but a million new signups ain't chopped liver. Year on year, Twitter's base of monthly active users went from 185 million to 241 million. Costolo may have offered a convoluted mea culpa about new users to analysts about boosting that growth — "We have a plan to make a broader audience to get Twitter more broadly". But focusing on getting your mom to use Twitter may mean you're missing a bigger problem closer to home.
The fact is that something happened in the fourth quarter that reduced a key metric: timeline impressions. Or to put that in English, Twitter users are using Twitter less. The number of times people look at their lists of incoming tweets dropped for the first time in at least two years, maybe ever. Check it out:

Fewer views: not good news.
Image: Twitter
It doesn't take Sherlock-style deduction to recall what happened in the fourth quarter: Twitter underwent a surprising number of redesigns. This was when the infamous "blue lines" really kicked in, confusing Twitter's reverse-chronological approach for the first time. If you were following two people having a conversation, you started to see that entire conversation repeated, over and over, every time one of them had something to add.
What made the blue lines exponentially worse was Twitter's change that automatically loads pictures for you, so you see them in-line without having to tap on them. This may be a pretty neat idea in itself. But combine it with the blue lines set-up, and the repetition gets obnoxious. If someone takes a picture at a sports game, say, and a dozen of your friends comment on it, you will see that picture a dozen times.
The blue lines were a prime example of a change that was supposed to make it easier for new users, but that Twitter's current customers hate. (I'd even dispute that new users find them worthwhile, and would like to challenge Twitter to show us any A/B testing that proves otherwise.)
Then there are what I like to think of as the dingbats — the little symbols for favoriting, replying and retweeting that now adorn every single tweet on the web and on mobile. You can't get rid of them.
Dingbats were also supposed to make it easier for a new user — hey, look, here are all the things you can do with a tweet in a single touch! But the fact is they look confusing and gaudy repeated over and over, as if your timeline was printed on Christmas wrapping. Only a coastal elitist would think that's the sort of thing that attracts middle America. Mr. Costolo, tear down these dingbats.
Anecdotally, it also seems a lot of users have been seeing more promoted tweets in the fourth quarter, which would make sense given Twitter's increased advertising revenue per user. I'm inclined to think this isn't such a big deal as the more fundamental design changes. Promoted tweets seem infrequent and innocuous, but maybe that's because I knew they were coming and was steeling myself for worse.
See also: Twitter's Promoted Accounts Coming to Your Mobile Timeline
Costolo is unlikely to address the design change problem, unfortunately, because these "fixes" fit into the narrative he is weaving for Wall Street — that he's going to turn Twitter into a super-visual, Facebook-style extravaganza. He's cherry-picking the data and notes that the number of favorites is going up — cool, to be sure, but does it matter when we're less engaged with the overall product to the point where we're refreshing it less?
For the first time on the analyst call, Costolo talked of an upcoming change where you get to "fix" the reverse-chronological timeline itself. In other words, the one thing that makes Twitter different, that wonderful sense of urgency and of being up-to-the-second, may be on the chopping block — replaced by the kind of algorithm that Facebook uses to determine what posts it thinks you'll most want to read.
But you can't beat Facebook by becoming Facebook lite. Rather, I would urge Costolo to consider that he has built a solid user base of news junkies, and that there are more of us out there than you might credit. I would venture to say that everyone is a potential news junkie for certain kinds of news. Your mileage may vary, and Twitter's strength is in how well it can adapt its news to your whims.
Sure, there's a small learning curve as you build up your stream, but you're never going to avoid that. Even Facebook has a learning curve. The shot of adrenaline you get when you realize you have the most important things in the world to you at your fingertips can be just as powerful in its own way as the joy of having all your friends' doings at your fingertips — more so, because the important things are being spoken and reported on right this second.
Even if new users do love the dingbats and the blue lines with in-line photos, and I don't believe they actually do, is it worth it? What shall it profit a company if it picks up two or three or ten million new users, but lose the respect of those 240 million monthly actives?