Threading is the idea that comments that reply to another comment should be placed indented under that comment, rather than at the end of the thread.
Threading is used by such sites as Google Wave (I have invites), znet, slashdot, and stuffwhitepeoplelike.
The reasons for threading are:
Better organization - it's easier to follow conversations and discussions when it's clearly indented under another post.
Ability to jump into a conversation for a late comer - For a personal example, I was involved in a thread where there was debate over RinxShirou vs SakuraxShirou. By the time I arrived at the thread, the RinxShirou portion of the discussion was over, and people were debating on SaberxShirou. In a linear/flat system, arguing against SakuraxShirou would be strange, as nobody seems to care anymore. But in a hierarchical/nested/threaded system, I can reply directly to the older comments and restart the conversation from where it left off, without interrupting the current conversation about SaberxShirou.
Ability to dismiss tangents - When people go on tangents in threads, as they frequently do, the tangents are nested under the higher level comments. People who cares about the tangential conversation can easily follow through the nesting system. On the other hand, people who do not care, and is only concerned with the original topic can easily see which comments fall under that tangent and ignore it. It also helps that these side conversations are hidden initially under the 'show' button. In a flat system, you would have to scroll down through all the comments, reading each one, to figure out which ones are tangential.
For people who want a flat system instead of the threaded system, please post here your reasons. We'll probably do a poll sometime later after everyone had a chance to make their arguments.
The threaded system is the default for now.
If people like the threaded system but want to see a slightly different implementation, or make some design suggestions, please make a new feedback post. This feedback post is for pros and cons of the threaded system.
Thanks.
Threading
10:09 pm 22/01/2010
The project that this feedback is for:
ThisWebsite Type:
Let's talk about... Status:
Resolved 
Comments
I'd actually be very interested to see why people oppose it.
One more thing, with threaded systems (especially prevalent with Slashdot articles) I get some system slow down if I have more than about 2/3 pages open because of the sheer amount of stuff on the page (makes scrolling down very slow and difficult).
Good points you're making.
Please give it a little time. Clearly people automatically prefer the way things have always been done, but sometimes there can be worthwhile changes.
I don't see why you can't do the same thing on a threaded page.
Slashdot set an inordinate number of posts to appear on one page. We certainly don't have to do the same. I can set only 10 top level replies on one page.
Also I think our pages are a lot more 'lite' than slashdot.
I dunno even what "genius" came up with the idea. But when I hear, that the way which has been always used by millions and with which millions are happy is that bad I find that a dumb and arrogant statement. Just my 2 cents, peace~