The VASER uses low energy ultrasound to disrupt the fat cells, while preserving other tissues, like nerves and blood vessels. This results in less discomfort (usually) and less bruising (almost always) than with other methods. The preservation of blood vessels is also very important (in my opinion) for another reason--if you require or desire surgery in the same area later in life, having preserved these blood vessels will mean that you will heal better and have a lower risk of complications.
Laser assisted liposuction is supposed to (according to the companies that produce the devices) produce less bruising because the laser coagulates the blood vessels (meaning that the laser burns them and obliterates them). While it may be true that this causes less bruising, I would not agree that it is less traumatic (a procedure that causes obliteration of blood vessels is more traumatic than one that preserves them).
The other claim often made by the laser companies is that the laser assisted liposuction units cause skin tightening. Again, it may be true that some minor amount of skin tightening occurs, but there is no evidence that it is more than you would see with a VASER treatment (or with Tumescent liposuction, for that matter).
I think what often gets lost in the argument about these new and very expensive technologies is that the real question is not whether or not the new device (like Smartlipo) can be done, but whether it is better, safer, and more effective than options already available (like the VASER). Having used all of the currently available technologies, I think that the answer is NO, laser-assisted liposuction is NOT better, safer, or more effective than other options available.
In fact, because the laser is much more likely to burn whatever you point it at (while the VASER is very specific for fat), my opinion is that laser assisted technologies are LESS safe, and sooner or later we are all going to start hearing about laser burns. Additionally, it's not as effective either (you almost always have to follow Smartlipo with VASER or tumescent lipo in order to get the desired improvement, unless you are treating a very small area.
These are the reasons I actually got rid of my laser-assisted lipo device and kept my VASER.
I hope that helps.