Thanks Tubbs.
Obviously any exercise that causes discomfort should be avoided. However, many exercises can be modified slightly and still be of benefit. Here is where dumbell work can be particularly beneficial over machines that have a "preset" direction of motion.
For example, if lateral raises cause you discomfort, simply changing the arc (direction) of motion or even the position of your hands may still allow them to be done. For example, when my own subacromial joint acts up, lateral raises are a killer. I modify it to lower weights, and then hold the dumbell differently. In this case, I satrt with my hands facing backwards (palm back, with forearm pronated) and arc straight out to the side. The dumbell stays perfectly parallel to the plane of my body. Range of motion is less, but it torches the delt and causes no impingement pain.
For barbell work, varying grip width may be of benefit also. I'll usually drop out incline benching and do more declines, which place much less stress on the subacromial space. I'll also drop out front squats (the ultimate subacromial crusher!).
Just play around with it, but start out light and give yourself LOTS of time to recover. You WILL get there again, I promise. As Randy (Macho MAN) Savage once told me during a squat session at Mid-City Gym in NYC: "Know your body and survive."