I'm a big fan of the touch-screen controller idea now. It just seems so... unique. And yeah, they have had problems in the past with such things, but its not absurd to think Nintendo figured away around 'em. I mean, surely finding a way to let you clean off a screen after/during play time isn't that difficult. Games that can have completely custom control schemes, or games where the controls are moving/changing as you play sound pretty interesting to me. I think I remember stuff like that being tried before, but never in something like a GameBoy. Definately makes this thing sound like more of a 3rd pillar than just a GBA 1.5. And if its pressure sensitive it even sorta solves the problem of analogue control in handhelds.
In any case, it makes thing more exciting. It's got a lot more people excited about the DS it seems too.