Is a deviated septum surgery usually done under local anesthetic or general anesthesia?

General usually. Surgery for a deviated septum can be relatively simple or complicated and is often combined with other procedures such as treatment of the turbinates or the sinuses for breathing improvement. Also the other nasal cartilages/bone may be shaped to alter the appearance of the nose. Typically general anesthesia is used for comfort, control, and to protect your airway from bleeding.
Depends. Can be done under sedation or general, and choice is based on the patient, patient's airway , surgical skills and preferences, location traditions and anesthesiologists training.
Septoplasty. Septoplasty is performed under general anesthesia. Be sure to have your nose evaluated by a board certified otolaryngologist.