This is an interesting little report from Wired.
Apparently, the iPad wifi+3G has a proximity sensor in it that’s meant to attenuate the signal from the 3G antenna. The way it works, according to the report, is that when the iPad comes into close proximity with a solid object (such as human flesh) it kicks down the signal a bit.
What this does is reduce the amount of radiation a person is exposed to if they are within close proximity of the iPad, so it’s designed as more of a safety feature. Whether or not that signal is bad, I’m far from qualified to answer, so I won’t go there.
Either way, the case tested by Wired is designed in a way so that it doesn’t trip the proximity sensor, and it redistributes the 3G signal away from the user’s body.
It’s an interesting read, and you can see about their testing and it even involves taking the iPad into an
Aperture Science Test Chamber anechoic chamber and testing the signal.
Have a look at the full report here.