Some UK researchers have studied the question on everyone's minds and found that it's true:
Your iPad is killing you.
People who use iPads for 4+ hours a day have a greater chance of dying than people who use them less than 2 hours a day.
The good news, such as it is, is that it's not just your iPad: Your TV is killing you, too. And your Mac. And your PC. And your iPhone. And all things that involve "screen time."
Basically, "recreational sitting," which is what it's called when you play Angry Birds on your iPad instead of say, throwing a baseball outside, increases your odds of having a "mortality event." Interestingly, these increased odds of dying are not just due to your being fatter and more out of shape because you spend more time sitting on your butt.
Here's the summary from the Journal of the American College of Cardiology:
Conclusions: Recreational sitting, as reflected by television/screen viewing time, is related to raised mortality and CVD [cardio-vascular disease] risk regardless of physical activity participation. Inflammatory and metabolic risk factors partly explain this relationship.