Splenda, aka sucralose, is made by replacing three carbon atoms in sugar with chlorine atoms. The theory is it's safe because your body doesn't absorb it, however various studies proved otherwise. Most of it that does get absorbed is metabolized and sent out the kidneys, but a small percentage converts into various untested chlorinated-saccharides.
So there. No better or worst than aspartame (Nutrasweet). Heck, try googling Aspartame and Rumsfeld sometime. Not trying to cause a political flame war, but there is some serious bad voodoo in the artificial sweetener business, and I'm not talking about the medical aspects here.
Ok, in the end, I drink diet soda occasionally, but drinking gobs of it everyday probably adds up to sometime bad.
-Steve