See http://code.google.com/p/lesswrong/issues/detail?id=301 for detail.
Go to your Preferences page and "Show parent comments on /comments" to take advantage of this feature.
(Work done by John Simon, integrated by User:wmoore.)
This would probably be a bit complex, but it would be neat if chains of two or more replies (B replies to A, C replies to B) that are all (B and C) recent enough show up on /comments would get grouped into a single chain of three comments (A (B (C))) instead of first getting (B (C)) and then lower down getting (A (B ("click to show more"))).
This comment, currently at 0 karma, is currently hidden for me on the /comments listing behind a "load more comments (1 reply)" link under the parent comment from Stephen_Barnes.
Nice... works great for me.
When the same parent shows up multiple times on the comments page and I click the thumbs-up icon on a parent that isn't the topmost one on the page, the thumbs-up only goes green and the comment score goes up only on the topmost parent on the page and the one I clicked remains unchanged.
Also, this is useful and I like it, thanks.