In Short:

Nintendo released an annoucement that the SSBB errors people are getting is due to dirt and smoke getting into the system and getting on the lens. (One more reason for you smokers to stop XD)  SSBB is the first game to use dual layer DVD which needs the lens to be clean.  They said if you get the error they will clean the system for you free of charge, including shipping, etc. though this is only in Japan I'm sure it would apply here if the same thing happens.

The Article: 
Yesterday's report of a buggy firmware update procedure for Japanese Smash Bros. Brawl discs was apparently just the start of problems for Nintendo. Today, the company issued a statement about reported disc read errors for the game.

According to the statement, Nintendo has received complaints from Smash Bros. Brawl buyers of the Wii being unable to read their newly bought disc, or of videos chopping up during playback. These users claim to have had no such problems with past games.

Nintendo has come to the conclusion that the problem has to do with dust and tobacco building up on Wii laser units. This effects Smash Bros. Brawl while leaving other titles unaffected because the new fighter uses a dual layer DVD, which is apparently more sensitive to a dirty lens.

The problem can be fixed by simply cleaning the Wii drive lens. This is something that the masses are apparently incapable of doing, so the Nintendo has decided to clean Wii units that are sent to them, free of charge.

Those who need this service for their Japanese Wii will have to send their system, warranty card, and copy of Smash Bros. Brawl to a Nintendo service center in Kyoto. Nintendo will be paying for the shipping, so there's no loss for consumers, except for a one week period without Wii.

For more details, Japan-based readers should check out Nintendo's Smash Bros. error page.

This announcement applies only to the Japanese market.

The Link:

http://wii.ign.com/articles/849/849072p1.html 

You have to get the Wii itself fixed because of it? That sucks.

aren't there lens cleaners on the market? Can those be used? I'd rather buy that than lose my Wii for a week.

At least Nintendo will fix it for free. They've got great customer service.

And yes, you can clean it yourself most likely...but Nintendo is basically offering to fix it themselves for free because they think you, the customer, are going to break your Wii, and that won't be fun for anyone. 

RED RING OF DUST!?!?!?!?! haha, yeah just reminds me how Microsoft is fixing their systems.

Bump for it being news people should know.

 I dont think the normal cleaning disc thing works, the one I'm thinking you're talking about is the one with the brissles that you put the cleaning solution on and it cleans the lens, that wouldn't work with the Wii because of how the disc is inserted, the system is motorized but if you look on the front of the Wii where you insert the disc is 2 flap type things that are there to prevent things from getting in there, those would wipe off the cleaning solution as you inserted the cleaning disc, so it's pointless.

wow. that kinda sucks. does this mean i will have to blow in my wii prior to playing just like my nes?

 Haha not quite, unless you REALLY BLOW, and I mean to Kirby standards.  Either way it's not a huge issue and those people with that issue probably need to dust more to say the least, Swifer duster to the rescue!

Not really. Outside Japan Wii seems to be dustproof.