Despite the fact that 80% of the links I’ve posted in the past 36 hours have been about Twitter, honestly, I didn’t have much energy to write a piece about the design of the new Twitter iPhone app.

I was (and still am) an enormous fan of Tweetie 2.0. But I switched to Tweetbot in April and have scarcely touched the official iPhone Twitter app since.

Naturally, I download the new Twitter iPhone app yesterday and have been using it — mostly to get a feel for the new design and where Twitter is taking their service. This article by John Gruber about the new Twitter design expresses my thoughts exactly.

Tweetie was an amazing iPhone app. And part of what made it such a great Twitter app was the fact it was designed by a Twitter user. However, as others have been saying, the new Twitter iPhone app seems to be a 1:1 extension of the Twitter business model. If Tweetie was designed by a user, the new Twitter app was designed by Twitter’s senior management.

Twitter’s monthly new-user signups have increased 25% since the service became integrated in iOS 5. No doubt they are looking to: (a) define Twitter in a new way for their new users; and (b) integrate a sustainable revenue stream into that new definition.

Twitter is a mainstream service and it needs to appeal to mainstream users and it needs to sustain itself as a business. The new mobile and web designs are a clear banner of what the new Twitter is all about.

It seems to me that the Interactions tab under the “Connect” tab and the “Discover” tab both are the clearest example of this new Twitter.

• For the “Connect” tab, I am a bit surprised that they didn’t just call it “Interactions” and only show the Interactions view as the default. I could not find the current stats, but based on some older reports I’ve read the average Twitter user has less than 100 followers. With 100 followers you likely do not get a lot of mentions all the time. And mentions are a big part of what draw you into the app.

Nobody launches Twitter without also checking their mentions. And so, including more interactions — such as when your tweets have been favorited and/or retweeted, and when new people are following you — is all about increasing the amount of user-centered activity that bubbles up in order to give an extra hook to draw you into the app.

• The “Discover” tab is, presumably, where Twitter will be forming their primary revenue stream: promoted items.

On the New Twitter promo video, #Discover is touted as one of the great new features of the whole service. This (just like with the Interactions tab) is where Twitter becomes more “immersive”. Once you’ve read all the updates from those you follow, you can find more stories and links and ways to spend your time in the Discover tab.

Moreover, this is where Twitter will be able to post promoted stories, promoted trends, and promoted users. When I tap on a story to “view tweets about this story”, the first tweet about that story is usually a promoted tweet.

For me, personally, as a user, I don’t find the content in the Discover tab useful at all. The top stories are things I’m already aware of thanks to the other places I get my news. The top trends are completely worthless to me. And I’ve never really taken Twitter’s advice on who I should follow.

• Thirdly, the absence of a top-level tab for DMs is just as much about the new Twitter business model as the presence of the Discovery tab is.

Moving DMs inside the “Me” tab was surely a design decision made by the senior management. I think it is fair to assume that Twitter has analytics telling them that most users probably don’t use DMs often or at all. But, also, (as Dan Frommer pointed out) I think Twitter wants your messages to be public.

There could easily be five tabs on the bottom row of the Twitter app. They could have had a “More” tab instead of a “Me” tab, and allowed you to customize the tabs (the way it’s done on the iPod app). But no. They have buried DMs as a sub-menu item and given it the near-equivalent hierarchy as drafts, lists, and saved searches.

I think Ben Brooks is right in what he thinks Twitter for iPhone 4.0 and Twitter’s new-new design tells current users:

“We care more about new users and you finding more people to follow rather than about how everyone has been using Twitter in the past.”

When Twitter began it was about updating your status to whomever was following you. Now it’s about an entire platform where you connect with all sorts of people and brands, and where you find your news and stories and topics of discussion from the greater Twitter community. Twitter has a new model and it’s not nearly as centered around 140 characters as it used to be.