I assume you mean 12 oz of mixed solution, using the usual 1 tablespoon/gallon ratio?
If so, the amount of actual sanitizer in 12 oz is pretty small, and since it is a no-rinse sanitizer, it is safe to get some in your beer. I did a quick google search, and what I read was that one-step works by producing hydrogen peroxide, which will then break down into water and oxygen (so no big deal) and "the only residue is a thin film of minerals that are naturally found in most water supplies."
So it isn't going to kill you. As far as other effects, I seriously doubt the amount of sanitizer in 12 oz is enough to kill the yeast. As far as taste, my guess is someone else is going pop in and say they accidentally added way more to a batch of beer and it tasted fine.