The folks over at Google have dished a few details on Gingerbread (Android 3.0). The main feature is a new UI, which isn't drastically different from the old one. Icons will look a little different, the notification bar will look a little different, there will be new scroll effects and green accents, but nothing too different from current versions.
The other thing is that video chat will be more integrated into the operating system. While video chat on mobile phones isn't too popular yet, the point of doing this is to compete with Apple's Face Time. The last but the biggest new feature is the addition of VoIP on Google Voice services. This will be a big deal for tablets especially, if carriers allow it.