Lately I've found myself following deep threads of a discussion more and more distracting and/or derailing a conversation. I think folding threads out-of-sight could really improve the readability of the comments section.
On my laptop, I just scroll through quickly and it isn't a problem. Where this would be useful is on my iPod touch - which often doesn't re-render the contents of the screen when scrolling quickly.
And better than having paginated comments, as noted here: http://news.ycombinator.com/item?id=2132568