In sheet form, it's pretty good for damping the high frequency vibrations associated with large thin metal surfaces such as a metal electronics chassis or further damping of a breadboard laying on an optics table.
The thin bubble wrap used for packing small items also works well for damping vibrations from things like remore shutters and is cheap (important for those of us on a budget).
I'm using three layers under my shutter mount (which is just a panel meter that's been hacked to block the beam when the power is reversed).
I'm also using it instead of carpet or sorbothane in between the various layers of my table.
It is very important to have the proper static deflection when using sorbothane. My tests showed it could actually be worse than nothing if one used too much sorbothane. Their web site has lots of information on this. If my foggy memory serves I used about 50% deflection on sheets and 70 to 80% in hemispheres.
I guess this is good to mention. Just because you have some sorbothane in there does not mean it will be better than without it. IF properly designed, it can be much better. Again the design guide can be very helpful but it takes some playing with to understand the parameters and how they relate.