I just cast my first head, being super careful to glove up and put on my respirator and goggles. Everything went well... no major spills or chemical burns. Cast about 4 or 5 layers, took my respirator off... and I didn't really notice any fumes. At all.
I work with some pretty potent stuff at the factory I work at, so maybe I'm just desensitized to strong smells? I have a really sensitive nose and I was just surprised that I didn't notice the fumes from the resin. Aren't they supposed to be super noxious? =\
EDIT: I'm using Smooth Cast 200