I'm playing my ds and the screen is constanly getting smudgy. MAybe they can make screens that aren't so so sensitive to dust. Its like it attracts it to the screen and that isn't the only touch screen device that does that. Still, got to like it. definitely not love it.
But, I'm broke. I ain't got no money. Ain't got no fancy car. Don't live the life of a millionaire, or a movie star. Temptations by the way.
When my ds gets really smudgy I tend to use long lasting window cleaner! It works wonders and tends to keep the smudges at bay for a while. Apart from that, wet wipes also work well. But window cleaner is the way forward.
It's the oils from your fingers which do it, it's not good for the health of the screen either. Bust out some glad-wrap on it! Another thing that will work well is a TINY amount of methylated spirits, dilute with water, and just lightly wipe the screen with it. Be careful though! If you used heaps of it and left it on, it could be a bit corrosive. (glad-wrap is what we call it.. i think the US calls it saran wrap or something?.. clear plastic food wrap)
I've never had a problem with a dirty screen, and I have two DS's. Do you touch the screen with your fingers? Or keep it in a moist place where it can get wet or oily?? I just use the cloth that came with my sunglasses to wipe the screen, because it's very soft and won't scratch it.