The D23 Web site just released a few previews from the D23 Expo.
Also, Lou Mongello of the WDW Radio Show is going to be broadcasting LIVE from the D23 Expo at times. Keep an eye on http://wdwradiolive.com/ or http://www.ustream.tv/channel/wdw-radio-your-walt-disney-world-info-station to watch Lou's live updates.
If you want to join in the chat on WDW Radio LIVE, here are a few tips:
Go to http://www.ustream.tv/
At the top of the page, beside the green "Broadcast Now" button, is a Log In / Sign Up section.
Click "Sign Up"
Fill out your profile information (name, gender, country, postal code) and "submit"
the next step, (Importing Contacts and Send Twitter to Followers) you may skip (click the link at the bottom of the page) You're taken to a page to start setting up your first show. At this point, you can close the window from Ustream and go back to the chat window for Lou's live broadcast. Click in the chat bar at the bottom of the chat area and a screen pops up. Type in your Login and your Password from Ustream, submit, and you should be good to go. (thanks to Sandy McGowan for these instructions!)