I've heard a lot about this nutritional yeast....what exactly is it, what sort of flavour does it have? I've had a look for it at the local grocery store, and can't seem to find it anywhere (i'm in Australia). Maybe i might need to try a health food store??
Yes, your health food store is probably the best option. I get it in the bulk food section at my grocery store, but the bulk food is the remnants of the health food section!
It has a "cheesy" flavor (not really, if you have tasted melted cheese recently!), and it is used to give a cheesy flavor to many dishes. It is not necessary to this way of eating, but it is useful, and often tasty. I found the hardest part of giving up cheese were those times when the dish needed some sort of flavor boost--I would often throw some cheese in it to melt, to give it flavor. I like nutritional yeast for that. I also use it in my no-fat-added salad dressing.