Saurik pushes a Winterboard update today , that brings a few new feature to the app. You can now optimize your theme PNG images, which will make your theme load faster, and i highly recommend you to do so. Please note that, the PNG files that have been iPhone-optimized cannot be viewed on the computer unless they are first deoptimized. You can use Cydia to reinstall themes that have been optimize in order to revert to the originals.