i'm a little late to the party, but general rule of thumb, IS is good for camera shake and operator involuntary movement such as wind/hand/breathing, etc... As neuro said, it's great for static images. I will not however do any better job stopping motion blur or subject movement. So if you're doing more low light night scapes and product or macro, IS comes in smelling like a rose, but if your subject is people or whatever and you need to freeze action, the 135 buys you 1 extra stop of shutter, which may or may not stop the action depending on the subject and situation. Hope that helps.