gamepro have their impressions and a cool video of them playing, you can see Peachs Final smash and Bowsers (Giga bower)
http://www.gamepro.com/nintendo/wii/games/previews/139928.shtml
Gamespot have a 10 minute long video with a Nintendo rep playing and talking about the game.
http://uk.gamespot.com/video/928518/6180868/super-smash-bros-brawl-nintendo-media-summit-2007-demo-1
The rep mentions in that video that theAnimal crossing stage will be tied to your Wii's interneral clock - Play that stage at midnight and it will be midnight in the level, I wonder if its tied to the time of year for different seasons?
Imaging playing that stage on Christmas day so its covered in snow.
Also: The Nintendo rep mentions that that after you pick up a final smash it can be beaten out of you before you use it.