Actually the bittersweet and/or semisweet chocolates have higher contents of cocoa butter in them than milk chocolate.
To be exact, several sources (Alice Medrich in her book Bittersweet) recommends storing chocolate in airtight containers at temperatures around 70 degrees F in the absence of spices and other aromatic foods.
I store chocolate in the relatively cool basement. Once I have used it to make truffles, I store them in the freezer until I am ready to use them. Since the boxes hole 12, this is a 6 day supply for me and my wife. And I find that warm room temperatures bring out the taste better. Our kitchen rarely goes above 82.
But I have a strange aphasic quality that COLD TASTES GOOD.
I just love having a dark chocolate bar in the fridge, pulling out a piece, feeling the cold and the taste of it on my tongue and having it warm and melt as I chew it. It is miles and miles better than popping the same chocolate at room temperature into my mouth.
I store my chocolate in the very cold fridge, then let it warm a bit before I eat it. I don’t like hard, cold chocolate. I like it a bit softer. On the other hand, I don’t want it a melty puddle.
My house came with a wine fridge that stays at 55F. Since I store no more than 3 bottles at once (1 red, 1 white, 1 champagne), the remaining space is good for fruit, chocolate, anything that needs to be kept cool but not frigid.