Might have been interference with all those controllers, lights, and Wiis close together.
Also, I think certain people are more demanding than others. I've noticed issues with the motion control here and there, but my brain smooths the issues over pretty quick. Like sword fighting in Zelda is pretty innaccurate: It reads horizontal swipes as vertical ones and vice-versa, and the horizontal swipes don't match the direction you swing in...but in the end, it still feels more like I'm really sword fighting than when I'm pressing the A button, you know what I mean?
I've heard a lot of complaints about Super Monkey Ball. Have yet to play it though...actually I have yet to play much of anything.