Joystiq is carrying a story that the Xbox 360 team was divided into 2 teams upon completion of the console. The first team is working to reduce production costs of the console and the other half is hard at work on a portable console. I highly doubt we will see anything at E3, but that is definitely interesting news.
Source: [url=http://www.joystiq.com/2006/05/08/takahashi-microsoft-portable-coming-halfway-through-360s-lifes/]Joystiq[/url]