I always thought that Xcode produces the most compact PNG files but this not seems to be the case. Turns out that there is a tool that does better job at optimizing PNGs.
Manually optimizing images with ImageAlpha reduced entire application size by more than a half (33.4MB down to 16.3MB). Images alone were 65% smaller and were displayed 2.5 times quicker than Xcode-optimized ones.
Since Xcode conversion can be disabled and iOS supports standard PNGs, such big size and speed savings are possible in actual AppStore applications.
DIMZZY 