Steviol glycosides are the components in Stevia leaves that give then a sweet taste. They can be very sweet, in some cases 300 times sweeter than sugar.
I don think that low consumption of Steviol glycosides is dangerous - however not much work or testing been done on it. Stevia has some approval from WHO and the FDA who approved its use as GRAS (generally recognized as safe) by Coca-Cola and PepsiCo in 2008.
Coke will use stevia as Truvia in Spirte Select and Fanta Select, products that offer reduced sugar over the standard versions of the beverages.
It is probably too early to truly tell how safe stevia is, time will tell.
Sweet Things - Just Say No
As I said before I would use any substance that maintained or encouraged the "sweet tooth" infrequently and with reluctance. This is because I think that it is better to reduce our tolerance for sweet things by avoiding them rather than sustaining the drive with lower calorie substitutes.