I'm passing on the Wii this year, but for anyone wondering/worrying about riots at Best Buy on Launch Day right at store open...don't. Sure, here or there you'll encounter a minor scuffle based on some ****ers trying to get 'cute' and 'meet' their 'friend' who's tenth in line, but there is NO WAY that Best Buy or any other retail store is going to allow for any sort of 'stampede scenario'. No. Way.
That said, some people might be willing to try some sort of trickery once in the store to ensure that they get their system sooner or can get to the games/accessories that they know will sell out the soonest. But once you get in the store and have your 'golden ticket', put it in your pocket and you'll be good.
The long sprint back to your car, though...just kidding. But please, be aware of shady types looming in the shadows. S*** happens every launch (although it's going to be an exponentially higher risk for those getting PS3s...glad I'm not going to be one of 'em).
P.S. This is just me, but if I were linesitting for the Wii, I'd get there no later than 8 hours before store opening, and even that might not be enough. It seems like every launch, especially in our eBay age, the stakes keep going up. There were many places where you were S.O.L. on the 360 if you weren't in line by noon the day before (and we're not talking about Midnight Openings, but instead 8 or 9 A.M. the next morning).
EDIT: P.P.S. And just like the inevitable shortages every launch, you're going to hear dozens of people with the 'no worries, man' attitude. They also seem to be the people perplexed when they walk up to a line a city block long when they arrive two hours before store open (very 'Eric Cartman' of them). Don't listen to them. They don't really know what they're talking about. Err on the side of Caution. Better safe than...you get the idea.
EDIT 2: Electric Bogaloo: Here's an even better idea: just preorder at a gaming store as soon as they start taking them. Call, get your name and number on their pre-preorder list and be ready to get there ASAP when the call comes.