Can you get hooked on diet soda?

Can you get hooked on diet soda? - CNN.com
Most diet-soda drinkers aren't as gung ho as Talles, but people who down several diet sodas per day are hardly rare. Government surveys have found that people who drink diet beverages average more than 26 ounces per day (some drink far more) and that 3% of diet-soda drinkers have at least four daily.

Are these diet-soda fiends true addicts? And if so, what are they addicted to? The most obvious answer is caffeine -- but that doesn't explain the many die-hard diet drinkers who prefer caffeine-free varieties.