When saving PNG files, I reckon we should be able to turn the gamma setting off. The reason being: IE7 changes the colours the image renders as, read here for more info. It's the only time Internet Explorer has stuck to a standard and had everyone hate it for it. Ironic, isn't it!
Anyway, if you can even just add a gamma-less entry into the filetypes box, it will save me having to use TweakPNG on every picture before it hits the net.