I don't know why this never occurred to me before. I wonder if gnus can
or will ever be able to do this.

1. I get a message in my 'misc' folder.
2. I move the message to 'misc.some-project'.
3. I reply to the sender (from misc.some-project).
4. The sender replies to my message which is filed by nnsplit-fancy in
   my 'misc' folder.

Repeat until you forget to move one and then you can never bleeding find it.

Alas, there's nothing about these messages that would make a good
split target. Except of course for all that nice In-reply-to threading
information so helpfully preserved.

Is it possible to get gnus to file the replies (step 4) in the correct
folder based on the fact that that's where the rest of the thread is?

                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | Our years, our debts, and our enemies
http://nwalsh.com/            | are always more numerous than we
                              | imagine.--Charles Nodier