Ultherapy is a fairly new device in the U.S. market (Fall 2009), although it has been in Asia for several years. Here in the U.S. the initial reports (from the FDA clinical trials) examined the effects of the treatments and showed that the results lasted for a year. Of course, since it is a new technology, we need studies that go beyond one year to see exactly how long the effective results can truly last. Informal reports from physicians who have been using this device for over a year, have reported effects lasting 1.5 years and more.
Having said that, it is very important to remember that neither this treatment or ANY surgery can stop time and the effects of aging. Even a face lift will have an "expiration date" (so to speak). Of course, the fact that you "reset the stage" by lifting the skin and muscle back closer to where it used to be means that even as you age, you are still ahead of where you would have been if you did not have any treatment at all.
Hope this helps!