I went to a Xmas party at a friend's place this weekend, and he had a bunch of people over, many of whom brought kids. I sat for a while in his home theatre room and watched 3 boys of ages 8-to-10 pick up the Wii for the first time. Amazing how fast they took to it.
In fact, the only thing they had any problem with was the qwerty keyboard layout when entering their name, as they weren't computer-savvy kids. Everything else was easily picked up.
Then they started Wii Sports boxing and all heck broke loose! No broken straps though.
Nintendo really has built something wonderful here. I was really skeptical about the controller, but am coming around. I still think it will have issues for long bouts of gameplay, but maybe gaming in 15 minute bursts, along with a play style that doesn't fit the preconceived notions about gaming, are just what we need to attract new gamers (or the 'dormant' gamers).
If you have any doubt, just have a look at the pool. Those are people have FUN!