Not sure if that link will work, but check it out on the New York Times's website under 'most popular' if it doesn't. I'm not horribly worried because I don't drink a whole lot of diet soda, but I'm sure there are some of us who have to have it for some guilt-free sweetness.
Anyway, don't want to be an alarmist, but I don't have a pubmed account (or whatever) so I can't read the whole article.
The first response hit it on the head: "correlation does not imply causation."
You have to understand that these studies are full of cofactors, which make it impossible to isolate one lifestyle-related phenomenon. For example, the idea that diets high in whole grains can help prevent heart disease came from a huge survey-based study of thousands of older women. What they found was that there was a slight trend that whole grain intake decreased risk of heart disease. Slam dunk, right? Well, not really because other lifestyle trends were not controlled, and it turns out that statistically speaking, women who eat more whole grains tended to be wealthier, more educated, non-smokers who exercised regularly. So why say that it was the whole grains? Well, because that's what they were testing, so that's what they wanted to find....
And this study is similar: obviously people who drink a lot of diet soda probably don't take good care of themselves in general, don't eat whole unprocessed foods, exercise, etc. So how can you isolate the diet soda? Sure, it probably doesn't help, but it's probably not the main culprit.
i think these studies are dangerous in that they encourage people to try to micromanage their well-being. Now, we are going to have people who stop drinking diet soda, thinking that they are somehow going to be better off, even though they are still eating like shit and sitting on their asses all day.
But, that's the problem with a nanny state trying to babysit its people. I think we would be a lot better off if we only did 2 things: 1) Stop subsidizing corn and soy so that junk food isn't artificially cheap, and 2) get rid of the nutritional guidelines, and just encourage people to eat real food.