What make/model cover do you have? I have the Apple one and it wipes clean with no problems at all.
The Apple cover/case is a perfect example of the 'saying' that "white dust sticks to black clothes and black dust sticks to white clothes". It's got a black faux suede finish, soft but it picks up dust very easily. However, as I mentioned, it wipes clean with a slightly damp cloth.
The edge of the cover is a slightly annoying 'seam' but one that Forum members have found acts as a (unintentional?) protection against drops. It's not as good looking as the new iPad2 Smart Cover but it's a tight fit and doesn't add much to the size or weight.
The downside is that, if you use the Apple Keyboard Dock for the iPad, you have to remove the iPad from this cover before you can insert it into the dock and, being such a tight fit, that's awkward and time consuming.
Hope you're enjoying your iPad.
Without trying to sound snarky, invest in a quality case. I use a customized Moleskine-style case from Treegloo, and the vinyl surface does not attract or retain dust at all, and easy to maintain.
I had a leather smart cover for my "2" (which I've put aside because my new Logitech/Zaggmate showed up). I'm old school. When Hartmann luggage was all the rage for roadwarriers, the more beat up your shoulder hanging suit bag was, the better. I didn't go out of my way to stain the smart cover, but it didn't bother me a bit when some coffee or jelly got on it