[Paint extremely slow or not responding]

If possible than try to upgrade your system.

[JPG quality: Paint.net vs Photoshop]

paint.net is useful for making small pieces here and there, and is a great improvement over the paint. But even compared to Photoshop in functions.

[Save As PNG results in bad file]

I think these results show that the registration of your images as PNG-24 can be a better alternative to save the photo in JPEG format with a quality of 100 at times. PNG preserves the quality of the discharge on the Internet. The only drawback I can see to save your image in PNG format is that some photo sites/galleries will not let you download it there, PNG, JPEG, etc.

[Pixel Competition #6 Discussion - Entry Period has Begun!]

I think there is no need to extend the date. Because the above design is upto the mark to claim the prize. Congrats in advance.