Styrofoam or Ceramic? That is the question.

Since the green revolution has begun I have been under the impression that reusable is always better. When you posed this question to us I was certain I already knew the answer. I was wrong. After doing some research I discovered that while ceramic mugs are great for hot drinks, you're actually not doing a big service to the environment by using one unless you use it 46 times before washing or rinsing it. This is because every time you wash your cup or mug, you are using water, electricity, and most likely non-biodegradable soap. In all seriousness my question is how many times could you reasonably reuse a styrofoam cup? At home I've begun keeping a nalgene bottle full of water in my refrigerator to keep from using a new glass every time I get a drink of water. At work I'm going to try a styrofoam cup challenge. How long can I reuse it? I'll keep you posted.