My findings:
Preparations:
Before anything else, make 100% sure you have version 3.1 firmware on your cube (can be seen in settings). You can get this through Mario Galaxy in the region you're from. Also, make sure you have Wiikey 1.9g.
Let the entire patch on this disc install and get dual channels (except for japanese wii's). I have been playing this game for 5 hours straight and I have not met ONE difference from how my Wii was before, so there is no problem with the update for your wii, other than that you have 2 extra channels.
Also, for PAL users, make sure you have put your Wii on 50Hz in the settings before you start the game.
Starting the game:
After you did all of the above, start the game. If you notice any shaking in the warning or loading screen, just reset your game, since you won't be able to play it properly (this occurs every few times). When you see no shaking, continue. You can let the entire intro movie roll. As far as I know, this and the first movie from the SSE mode are the only movies you'll be able to see without crashing your Wii.
A translation of pretty much all the menu stuff can be found here:
http://faqs.ign.com/articles/849/849163p1.html
Playing the game:
I have not tried everything, but I can say the following things with 100% certainty.
- VS mode works, however, it crashes every now and then (occured about 5 times in 5 hours for me). If you keep your battles reasonably short, it shouldn't occur too often (5 stocks for example).
- Classic mode works, but it will crash after the credits.
- You can play the Target minigames. Possible other minigames as well, haven't tried those however.
- You can unlock at least 4 characters through battling. (Luigi = not sure, just quite a bunch of matches I think, Marth = same, but less matches, possible involving Ike, Snake = play 10 battles in Snake's level, Ness = play 5 matches in VS)
That's pretty much all the info I can come up with, for now
If you have any questions, feel free to ask.