Wow! 1/2 a teaspoon might be pushing it ... maybe not for big beers though. I made a 5wall gallon batch of .060 using 1/2 tsp and it made the beer taste like vegemite(sp?)
Yeck... an acquired taste I guess... and I don't want to acquire it. Lol!
Some types of yeast nutrient comes from autolyzed yeast, which is where vegemite comes from. In fact, I was at a brewery and they pulled some yeast from the bottom of a conical and added it to the boil to create their own yeast nutrient. I'm planning to do the same from my fermenter this weekend. When did you put in the yeast nutrient, Dean?