First, I'd like to point out that this isn't just a Droid X problem. I've done a fair bit of reading and similar issues exist with the D2, Incredible, iPhone4, etc etc.
But, for those still having issues, here's some interesting info:
A friend of mine with a D2 was having this same problem. He plugged into his motorola wall charger that came with his phone and his touch screen would go wacko. Unplugged it, worked perfectly. He plugged the usb charger cable into his laptop, worked fine. I attached MY D2 to his wall charger, and it did the same thing, the touch screen would go wacko.
Well, it turns out, he had the wall charger plugged into a power bar right beside a cheap ebay Ipod charger (see pic attached). We tried moving the ipod charger and the problem went away. Even with iPod plugged in right next to the motorola charger, the only time the problem would happen is if the ipod was drawing current, making the charger actually do some work. The fully charged ipod with the screen off wouldn't cause the problem, but if the screen was on, it would.
The cheapo ipod charger was interfering (EMI) with the motorola one. we separated them and all is good now. You'd think phone manufacturers woudl included better EMI shielding or charge cable regulation/filtering inside the phone etc, but i guess thats pretty low on the priority list in such a competitive industry...
Anyway, just something to try if you're having problems....