Twitter blog :: Starting today you can make your presence on Twitter more meaningful with new Twitter profiles. Upload an all-new header photo on mobile apps for iPad, iPhone and Android or twitter.com, and the same image will appear whenever anyone views your profile on the web or these apps. You can upload your header photo, which appears above your Tweets, to express yourself instantly, anywhere.
Read (incl. screenshots:) Sachin Agarwal, blog.twitter.com
2nd update: "Picture what's happening in iPhone and Android updates" - Read Jaikumar Ramanathan, blog.twitter.com
3rd update: "Expand your experience: New Twitter for iPad" - Read Sung Hu Kim, blog.twitter.com
A nice overview: "Twitter announces new profile pages, iPad app" - Read Wilson Rothman, digitallife.today.com