I am an advocate against using sugar substitutes. Natural sugar is something that your body can break down and use. I understand those people who have diabetes because before prior diagnosis, the person went on a sugar overload and overwhelmed the body with sugar and your body doesn't know what to do with it. However, this does not mean that artificial sweeteners are the route to take, in my opinion. I understand that diabetics are able to have SOME sugar/carbs in their diet, and that should be the boundary that you should follow. Anything more should not be consumed.
As for "lack of research," a quick Google scholar search turned up a whole host of peer reviewed journal articles of empirical research on the effects of artificial sweeteners. The one that I read covered a few bases of the effects of artificial sweeteners such as the lack of a "I am full" enzyme, increased BMI in both youth and adults, increased sugar dependency, and limited energy resulting from consumption.
The explanation of Stripes237 on how they "heard somewhere" (Skellig19) on how diet sodas stimulates appetite is explained in this article. It basically says that normal food has a built in indicator that is broken down in your digestive system and sends a signal to your brain saying that "I am full," basic A&P (anatomy and physiology). In diet sodas, not only does it not have any calories (the number of calories contribute to the strength of the "I am full" signal), but the ingredients itself, namely artificial sweeteners, do not have the signal indicating to stop eating/drinking.
For arguments sake, since water does not have any ingredients in it, there are several ways the signal goes into your brain. But the most reliable one is the one at the start of your intestines measuring the caloric intake and the necessary chemicals to trigger your brain.
Dunno if this link will work, but this is the article that I cited in this post.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2892765/