I found today that Internet Explorer doesn't handle PNG files very well. I suppose I should clarify. Internet Explorer 6.0 and I am assuming previous versions display transparency incorrectly. They also don't handle color mapped PNG-8 files well either. I found the PNG-8 files look like Atari graphics (very blocky) where as in Firefox and even Windows Image Viewer they look correct. I.E. does handle GIF and GIF with tranparency correctly or as one would expect.
I love Firefox more and more every day. It makes creating a web application so much easier, except for having to still support Internet Explorer which sticks us in the pre-PNG days. For instance, if we could use transparency in PNGs correctly we could use high resolution icons/graphics with drop shadows and the like and not be locked into specific background colors thus making working with Cascading Style Sheets all the much easier. Currently this is not possible because of Internet Explorer. End Rant.