Stevia is safe for people with diabetes and it is known to protected against cavities. It comes in the natural powder form (green), liquid, and extracted white powder.
The only caution I have ever heard is to be sure of the source of the extract because it can be effected by the processing, often completed with toxic substances.
Now that Big AG (Cargill) and megacorp CocaCola are involved it seems more like they want to control the market rather than serve the needs of people who want a safe sugar alternative (aspartame, acesulfame K and sucralose are not).
Other choices are Just Like Sugar and Agave. I encourage caution on large amounts of xylitol.
Is stevia a safe sweetener?
From the November 2008 Issue, SELF
Ask a Food & Diet Question
By Joy Bauer, R.D.
It's unclear. This zero-calorie sugar alternative is all natural (it's made from a South American shrub), but the FDA has not granted it "generally recognized as safe" (GRAS) status. The reason? Research on stevia has raised concerns about its effect on the cardiovascular and reproductive systems. The Center for Science in the Public Interest in Washington, D.C., agrees with the FDA and has called for more testing. But recent human studies indicate that stevia may lower blood pressure and benefit people with diabetes. I have a hunch that the FDA may soon approve one stevia-derived product called Truvia. It is made with rebiana, a purified component of stevia, and is produced by two mega foodmakers, Cargill and The Coca-Cola Company. If Truvia is deemed GRAS, and you like the flavor (some say stevia tastes like licorice), consider using it, but when it comes to stevia in other forms (it's sold as a supplement in health food stores), your best bet is to wait for the green light from the FDA.