If you’re not using Smush.it download it now. No respectable web designer can avoid this amazing firefox extension.
Smush.it strips out all the extra data that photoshop leaves in. None of the data effects the visual quality of the image. A quick survey of my sites show that PNG files created by photoshop can save from 25 to 50% of their files size. INSANE!
What kind of saving have you gotten from your sites?