Here is an idea for Paint.net.
Batch image converting.
Searching for a good program that does batch converting of images but can't find anything that does it or it's for private use only (not even mentioning non-commercial or other stuff).
Having this in Paint.net would be very useful, especially since even Gimp doesn't do it.
Something that goes like this would be nice: Choosing directory and/or separatelly images. choosing what formats to convert to what (eg png to jpg), choosing quality and output folder(s) and press OK. 8)