First, please expand this rule to cellphones and smart phone devices like Blackberries. People checking their email constantly means they aren't paying attention and is distracting. They then have to have things repeated which lengthens the already long meeting.

Second, what about wi-fi free meeting rooms. Or just turn off the wi-fi during important meetings. They can still take notes, but can't surf the web, check email, or do anything except maybe play games.