As another test I used some digital inputs, when I press the left button "A IS ON" is displayed on the LCD, when I press the right button "B IS ON" is display, even though you can't make out the text, you can see in this video that just being near the button makes the Arduino sense enough voltage to indicate the button is pressed and display some text...
http://www.youtube.com/watch?v=jKuIDsq0WIQ
OMGWTFBBQ?
I have forgotten how I wired that pot but I ripped it all apart and started over with this small test but the problem still persists?
Is interference really that big a deal on these small circuits? To answer your question, it is powered off of a front USB socket on my PC, but I plugged it in the back and got the same result. I also tried unplugging all other USB devices, turning off my monitors and speakers to that just the computer was on giving the Arduino power but it is still going mad for EMI.
I turned my PC off and the main power socket so everything in the room went off, and ran the Arduino off of my laptop so it was using the laptop battery, same result. I used a 9v batter, same result!
If my Arduino is this susceptible to EMI its pretty much useless.