We would strongly recommend that you registered separate accounts for your dev, test and live and keep the API keys separate. From our end, we do not differentiate between your accounts. However if you use the same key for all of your services, you will have a single rate limit of 600 per 5 mins. If your dev system ran away and used up all of your 'rate limit' allowance, your live account would stop working of course.
Hope that helps.