Threading: Mail.app vs. Thunderbird
I generally prefer message forums over mailing lists for community discussions because of the better separation of topics and implicit threading. Not that forums are ideal for threads, since they generally cannot easily spawn sub-threads.
So, when reading discussions on mailing lists, I try to use the threading mode of the mail client to bring some clarity to the discussion and filter out discussions I don't care about. I am a big Imap proponent and read mail on PC with Thunderbird and Mail.app on Mac. Overall i like Mail.app better but sometimes it does exhibit the Mac app tendency of "if you don't like the way we do things, well, sucks for you", vs. Thunderbird's more liberal configurability.
I'll leave the whole subject of how well clients group messages into threads.... Ok, just one stab at that subject. Subject of "Hey" is not too uncommon. So all messages of "Hey", which are almost guaranteed to be unrelated, get lumped into a thread together. Happens in both readers. I know that threading in mail is ad-hoc, so I am not faulting the clients. It's just a silly artifact.
But here's some behavior that I find not only unintuitive but downright tedious:
On both Mail.app and Thunderbird, i can collapse and expand threads by using left and right arrows. So when I decide that a discussion is not of interest to me, i just collapse the thread and hit delete. On Mail.app, the thread is deleted, as I'd expect. On Thunderbird, the current message in the thread is deleted and the next message becomes the head of the thread. So to delete a thread i have to open the thread, select all messages manually and then delete. Bah!
I've dug around the config and even advanced config, but can't find a way to change this behavior.