I've been using this on a few sites now and it rocks! Recommending it to be used by most of my clients. Why even waste your time caching or using a CDN if you haven't first done this? Photoshop is great for doing a great deal of stuff but the image optimization I easily achieve on top of my photoshop optimization is stellar! I see reductions in file size (for already optimized images) by between 20-70% and the images look great.
p.s. always test and backup your installation. Things can go wrong anytime you are manipulating so much data. I did have a few posts where the links had to be fixed, out of thousands of compressions so far. So no biggie.