For years, I have only used trn to read Usenet news. This is mostly because trn's thread display was really awesome; it would display the child articles to the right of the parent, and the siblings directly below each other, forming a sparse grid of sorts. For me, this was always much easier to grok than the nested list thread display that is used basically everywhere else, which neither allows you to clearly see which articles are siblings, nor which are parents in longer threads.
Including in the Thunderbird mail client, sadly.
I use Thunderbird because I'm a Linux guy and it's every bit as good as the next thing for my purposes. I access both my real mail and my gmail account through it, so why not Usenet news, as well? *grits teeth*
The short answer is that it's A-OK, if I can force myself past the tree-style thread view. It works just fine, and does things I really really wish trn did, like cache local copies of recent articles. (trn was written in a day when disk cost so much you wouldn't even consider locally caching the articles.)
Of course, now I was reading news in a modern GUI instead of a terminal program. And I noticed an interesting thing: some articles were "hard"-wrapped at about 72 columns, while others automatically wrapped to the width of the screen. My first thought was that these people were using busted clients that were behaving badly, but viewing the source of the article showed that it was cleanly wrapped at 72 columns! How did my client know to rewrap the paragraphs?
The answer is a little tag at the end of the Content-Type: header. But NNTP enthusiasts are saying at this point that NNTP didn't historically use that header, which is true enough. Modern clients, like Thunderbird, seem to put them in there, though, like this:
Content-Type: text/plain; charset=ISO-8859-1
With a tag like that, newsreaders will behave in normal mode (MST3K: "NORMAL MODE! NORMAL MODE!") and not rewrap anything, but if you put this in, instead:
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
the newsreader will do its best to rewrap the text, including comments.
In Thunderbird, you can control both whether format=flowed is set on your outgoing messages, and whether it is obeyed on incoming messages. This is done through the mega tuning menu which can be found in Thunderbird under Preferences→General→Config Editor. Type "flowed" into the search box, and you should see two options:
(Yes, it's weird that one of these options has a negative sense while the other has a positive sense. But then again, this config section was never meant for general consumption.)
At the end of the day, I decided that format=flowed was a good thing, but I couldn't stand looking at the ultra-wide output on my maximized window, so I turned off display_format_flowed_support, and there we are.