Installed but could never use it initially. That said, it may not work with your system without some major tweaks. I kept getting this error: "EWWW Image Optimizer requires jpegtran, optipng or pngout, and gifsicle. You are missing: jpegtran, optipng, gifsicle. Please install via the Settings Page. If the one-click install links don't work for you, try the Installation Instructions."
Definitely makes the install very un-user-friendly and from the looks of the forums I'm not the only one who has had this problem.
To fix the problems read the installation instructions for this plugin first.