Twitter have just launched a new re-design. Here's a first look:

We’ve simplified the design to make it easier than ever to follow what you care about, connect with others and discover something new. You’ll see this new design both on Twitter.com and mobile phones, so that you’ll have a familiar experience any time, anywhere. We’ve also updated TweetDeck to be consistent with this new version.

 
A first look at Twitter’s redesign

Update: Twitter have also changed how brand profiles work:

As part of this release, we are introducing enhanced profile pages that help marketers create an even more compelling destination on Twitter for their brands.

Now, your profile page does more to help you make an impression with a large header image for displaying your logo, tagline, and any other visuals.

You can also control the message visitors see when they first come to your profile page by promoting a Tweet to the top of your page’s timeline. This Tweet helps you highlight your most engaging and important content and better connect with your target audience. The Promoted Tweet on your profile page will appear auto-expanded so that visitors to your page can instantly see the photo or video content that you link to from your Tweet.

This page and the Promoted Tweet are both free of charge and publicly accessible for the whole world to see. Your profile page is your own - your colors, your logo, and your messaging.

 
Enhanced profile page

Update 2: Simon from We Are Social Singapore takes a look at the similarities between the new Twitter and Sina Weibo.