JPEGs, PNGs and GIFs all look great when used in the proper situation. The problem is when an individual uses a JPEG when he should've used a GIF and vice versa.

PNGs are totally useless in the web world. The support for this format is lacking and certain browsers do not support it at all. But, PNGs are great to import into Flash/Director when one needs an alpha channel for tranparent backgrounds or drop shadows.