Talk from TiPb and the Twitter indicates some improved features on the iPhone 3.1 have already been found.
Voice control works over Bluetooth, the iPhone vibrates when moving icons, the modem firmware has been updated to 5.08.01 and the AT&T profile has been updated to 4.2. You have the option if you wish to save as copy when trimming a clip on the video editing.
There are also some improvements behind the scenes as well, including changes to OpenGL and Quartzand APIs will now allow third party app to not only access videos but also edit them.
MMS buttons are back for AT&T users, but they are non-functional on standard devices as with the early iPhone 3.0 Betas. Whether or not they will survive to the official release this time is another question.
To find out more visit theiphoneblog.com