I like the fact that when I click the "show more comments" link under a post, that the previously hidden comments flash their backgrounds when they appear. I believe this flashing behavior is a relatively new feature.
And now on to my feature request - Can the backgrounds on the expanded comments permanently retain the flashed (highlight) color? This would make it easier to tell which comments were just expanded.
So if we look at this example image, we see the initial comments with a white background, and the expanded (previously hidden) comments permanently highlighted: