Well there are various questions to be asked of you first...

1. Is your Wii getting proper ventalation? There is a fan in the Wii meant to keep the Wii cool when you play for an extended amount of time. If you block the vent for the fan, then your Wii may be overheating.

2. Is there any sign of an abnormal amount of dirt around the Wii? For instance, do you or anyone else smoke around it? Is there a lot of dust where it is? If so, this may lead to leanse reader in the Wii getting covered in a film of that dirt and in return, the Wii has trouble reading discs.

3. Did you happen to kick the Wii out of frustration? I still see people spiking controllers when they are pissed with Madden or whatever game tickles your fancy. I'm hoping you weren't that stupid and kicked the Wii. Or possibly, is it in an area where it could have been accidently hit like that?

Besides those three, I don't know what to tell you. I know the Wii will be slow for SSBB because SSBB is made on a more complex disc than other Wii games. So, if its just SSBB that is giving you the problem. Don't sweat it. Check it out and put other games in it to see if the problem is universal. If not..check the manual, and pray to Reggie.