The hourly rate you should charge as a consultant depends on several factors such as the amount of days you can work a year, your overhead costs such as rent and the annual salary you want to make.
These factors vary from person to person, making hourly rates very personal.
Take your salary for instance. The salary you can earn depends on the level of experience you have and market situation for the industry you are in.
Sometimes you read about consultants asking for examples of hourly rates, only to receive a wide range of rates as answers. I agree, it is nice to know what others in your area are charging. However you have to realize that your personal situation is different from other consultants. The hourly rate you should be charging can be quite different from the consultant across the street!
Review Your Rates Regular
Your personal situation is something that is always changing, so it is good practice to for consultants to review their rates on a regular basis. Both starting and experienced consultants should do this.