It's PROBABLY quite safe but i would trust Aspartame or Cyclamate a lot more for daily use. But once a day in your tea would be be no problem with Stevia.
If producers submit testing to prove stevia safe enough for use, then it becomes a different story and they'll be able to put it in soda.
For a 5-can-a-day habit, be careful though. You might be getting a bit too much of WHICHEVER you choose, although probably any choice is better than 45 teaspoons of sugar (and the extra 100 pound weight gain

) that you would get from REGUALR soda.
Cut down to 4 and see how it goes...then maybe 3!
How do you like the taste of stevia in your tea? How does it compare to aspartame?