I purchased a head of garlic and I have 2/3's of it left over, I am storing it in the fridge in a ceramic covered dish (made specifically for garlic :) a gift from my mother) and I would like to know how long I can continue to expect fresh flavor from it. What would the garlic look like if it had indeed spoiled?
Garlic will spoil faster in the fridge actually. I don't know how long it will last in the fridge, but I understand that it lasts longer if you leave it in a cool, dark, dry storage. I believe one reason is that your fridge is generally too humid. In my experience, garlic kept in the fridge is also more likely to develop mould (goes soft, and dark discolouration).
I keep mine in a ceramic thing in one of my cupboards. It lasts anywhere from a few weeks to a few months depending on the garlic (probably how long it sat before getting to my kitchen). If you store it like that, garlic that goes "bad" will usually start to sprout (green shoots, will come through the top.
Garlic will hold amazingly well for a couple of months. I have one bulb without any protection whatsoever, although it's out of direct sunlight.
The cloves will 'go' one by one. Some will start to sprout. I guess this depends on the environment. Others will dry. Others will rot (black mold, it will turn to dust).
Discard the rotten ones and cut away the dry parts. But you can use the sprouted ones, just take the germ out.
At any rate, just buy the least amount you'll use (I buy one bulb at a time).