A couple notable statements about caffeine, they note that there isn't a lot of hard data about caffeine and its specific effects. It is clear that everyone has someone different reactions to it.
The only mention in one quote that it is 'generally accepted' to be an addictive substance, though again, from other articles that seems very unclear too.
It appears though that around 10g (10,000mg) of caffeine is the toxic dose for caffeine. A 16oz cup of drip-coffee from Starbucks has 330mg of caffeine in it. A 20oz Mountain Dew has only 90mg. So, that is a long-shot off of 10,000. 30 Starbucks coffees in just a few hours, or 110 Mountain Dews.