The ideal way to drink a smoothie is at room temperature. We originated in the tropics and in the tropics our fruit would be sweet and fresh off of the tree. When you chill or add ice to your smoothies it doesn't taste as sweet, I've noticed, probably because it numbs the inside of the mouth a bit. It is OK to add ice to them though or use frozen fruits, but it's not ideal.
I always make mine with cold water and ice, then blend...instead of adding ice after or putting it in the freezer/ fridge.