Dependency is the big one relevant to the OP. Withdrawal can impact energy, mood, cognitive function, and cause bad headaches, among other things, I'm sure. Caffeine use can also compromise sleep, raise blood pressure, and increase anxiety. Caffeine intoxication is an acute state and has a range of effects as well, but that's not really what you're asking about.
The wikipedia article actually has a good summary of some of these issues as well as others.
You'll notice that the higher dosages given in that article as being risk factors for things are within the range of 'several liters of iced tea.'
As an avid coffee-drinker - what are these effects? I've read upon caffeine and I've found no clear evidence for permanent harm or good out of coffee.