In a review of 23 studies of such treatment involving 1,053 patients, the researchers concluded that the therapy, given as often as three times a week, in many cases for more than a year, relieved symptoms of those problems significantly more than did some shorter-term therapies.
via nytimes.com
I think that we will begin to see more and more research done on longer term psychotherapies as a result of the shorter term therapies and medications only addressing the symptoms and resolving the underlying roots of what is causing individual to seek treatment in the first place.