Topic: When will people get it?
Fear not, it has nothing to do with the election. Here goes:
JPEG: Suitable for images with a large variety of colors and complex, irregular patterns. E.g. photographs, rendered images, drawings etc.
PNG/GIF: Suitable for images with fewer colors and variations and in particular, large areas of the same color. E.g. screenshots of GUI's, logotypes etc.
If in doubt, use PNG. I prefer a dithered PNG with fewer colors to JPEG artifacts. If I see one more GUI screenshot or logotype that has been jpegged beyond recognition, I don't know what I'll do. My eyes are still bleeding after visiting http://www.postgresql.org/ and looking at the logo at the top.
</rant>