In recent months, Velonews followed up with information from Stan's saying that their is an infinitesimal amount of ammonia currently in his fluid, and that its composition has changed over the years it has been in production.
While the pictures from the first Velonews article are very scary, I have been using sealant on my road tubeless rims for four years now. If there has been any corrosion, I haven't seen it. I have mostly been using Stan's, but I am also trying the Slime Pro product on one of my bicycles.
As an early adopter of road tubeless technology, my advice is to use your favorite sealant, relax, and enjoy the ride!