Forever burnt into my mind is PNG alpha work-arounds in IE:
filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src='image.png');Ha, fantastic line that one. Transparent pngs caused so much unnecessary trouble in IE6, it was very annoying, and limited our options as graphic designers.
Hah, my thought as well, was a part of my standard page setup. And then using those transparent pngs to do rounded borders with 9 images nested within 9 divs!
Edit: and down memory lane: the spacer.gif