The basic principles behind the ShakeWeight appear to be somewhat sound, however, the research displayed in their advertising is (likely intentionally) misleading. Their advertising states that a minute of exercise with the ShakeWeight is equivalent to 42 minutes of exericise with dumbells. What you don't see (or most people don't see) is the little print at the bottom that says that the study was done with the same weight in dumbbells as what the ShakeWeight weighs. For the men's version, this is 5 pounds, and for the women's version is only 2.5 pounds. I've never seen a man working out with only 5 pound dumbbells, personally.
Additionally, the ShakeWeight does not allow for a full range of motion exercise routine which will seriously limit the effectiveness of your muscles outside of the range in which they are being worked and could be seriously detrimental to future workout efforts not involving the ShakeWeight.
As far as "can you look like that guy?", no. The ShakeWeight is only designed to work your shoulders (deltoid and trapezius), arms (bicep, tricep, and forearms), chest (pecs), and upper back (lats and traps). It will not work your legs, lower back, abs, etc. You will still be required to work those muscles separately if you want to look like the guy in the commercials.
I'm fairly certain that you can use the ShakeWeight to go a certain distance in training the muscles I mentioned before, but scalability is going to eventually catch up to you, and likely quite quickly if you are really trying to build. Since you cannot increase the weight, you can only go faster to get more of a workout. There will come a point where you can't go faster, and the device will be too light. At that point, the device will become useless, and if you hope or plan to maintain any gains you have made or advance further, then you'll need to be prepared to devote some time to a normal workout routine. However, due to the lack of a full range of motion exercise, you'll be far more prone to injury when switching to standard weights.
My advice: Don't work out with it.