I read my iPad2 in bed pretty frequently, it's just heavy enough that resting the weight of the device on a single edge on your chest will become unpleasant rather quickly.
As an extra datapoint, a Kindle (170 grams) is trivial to lightly with a few fingers. It's no substitute for a tablet, but when all I want to do is read a book I love it so much more than any heavier, more capable device.
