I'm using Paint.NET pretty much ever it was first released to public and i just love it. Small, powerful, simple and free. But the "Save as..." dialog was getting on my nerves for quite some time now. The thing is, it works for what it was designed, the problem is that it doesn't work too well when your target is to get the best image quality at the smallest size. Sometimes JPEG creates the smallest file, other time its PNG. But you can't know that until you actually chose one filetype and then you get to the preview screen where you see the resulting file size and quality. And if you don't like it you have to repeat the whole proces of going into the File dropdown menu and selecting "Save as..." again.
Couldn't it be done in a way that "Save as..." dialog would contain all 4 features. Preview, file size, file type and save destination in the same dialog? So you can quickly switch between for example PNG or JPEG and see which produces the best results and when you see which one is the best you hit the Save button. Which makes image editing light years faster than if you have to open the dialog over and over again from scratch just to see which format creates the smallest file. Or having the Save destination being selected after you pick the image format and settings, not before it like it is now.