The initial "Hello Google Now" seems to ignore other voices, but the commands are a little picky. Earlier, my girlfriend and her sister were talking while I was playing with it, and it would pick them up every once in a while.
I've been using Touchless a lot, just to see how it works. The most "practical" use I've found is in the car. I've been connecting to my car radio via bluetooth, and mounting it on my windshield. Touchless then gives me full control with "Navigate to..." "Call..." "Send text to..." and "Play music by..."
Sometimes it will take more than once for the initial "Okay Google Now" but after that, it is very accurate.