I am unable to connect to my Wi-Fi at home, but am able to connect at work. Using my new iPad 4G with cellular and a Motorola SBG6580. My iPad 3G Wi-Fi only connects just fine; the 4G just "spins the gear."
Tom, I should have mentioned that I tried 1 and 2 but was unsuccessful. I was about to try 3 when I remembered having to contact CableOne (tv and internet provider) to get on with iPad 3G. So I called them again, and he took your suggestion to change channels, and also changed the name and password. I don't know if all that was necessary, but it was successful.
Of course, I had to change the settings on the 3G and the Apple TV, but all is good now.