In August 2008, Google released what was called the enhanced 404 widget that allowed webmasters to easily create custom 404 pages. In fact, we still have a sample of this in action at advertize.html.
But for some reason, I think Google removed the feature from the Google Webmaster Tools section. As a Google Webmaster Help thread discusses, he can't find it in the Webmaster Tools section. I looked for several minutes and I also cannot find it anywhere.
Did Google move it and I can't find it? Did they drop the feature with the launch of the new design?
Forum discussion at Google Webmaster Help.