There is evidence to suggest that the artifical sweeteners commonly found in diet drinks can cause an insulin reaction in the body.
It's a simple reaction to the sweetness, not carbs-- as there are no carbs in diet drinks. The body simply associates the taste of sweetness with the presence of carbs and assumes that carbs are present, increasing insulin levels in response.
I don't have the empirical data. I can't stand soda whether it be diet or sugary.
Drink water or unsweetened tea, coffee.
Aspartame "side effects" studies show all kinds of scary effects. I have read enough of these studies that lead me to believe there must be some concrete evidence that this substance truly is not good for you. Quite a few links available through the Google meister...