The use of a corporation or LLC will not generally protect a professional from liabilty resulting from his or her own professional errors, omissions and acts of professional negligence, or from such acts of other persons (employees) under his or her direct supervision.
Forming a corporation or LLC may protect you from contractual liabilities, such as your lease, the utilities, etc., if the entity is the party named in the contract. Smart landlords and other creditors will insist on your personal guarantee even if you operate as a corporation or LLC.
One of the best reasons to form a corporation or LLC is to protect owners from errors made by employees or other professionals in the same practice. If Joe down the hall commits malpractice, and you have not been involved in the client's matter, you will not be liable. This does not hold true if you practice as a general partnership. Rule of thumb: If you practice with someone else, form a corporation or LLC (or in some states, a limited liabilty partnership [LLP]).
If you practice by yourself, it is very easy to set-up a single member LLC (available in most states). This doesn't reduce your liability for tortious acts, but it helps you separate your personal business from your professional business. You might be able to get your lease, utilities, etc. only in the name of the entity. Tax preparation still requires a Schedule C. You can, if desired, obtain a separate tax identfication number.