I recently disabled threading in my email as I have an unfortunate number of people who regularly : send mail using identical subject lines, reply to whatever my previous email to them was rather than come up with a new subject line or send multiple versions of important documents under the same subject/RE the same message over the course of months. This results in a hideous nightmare of thread spaghetti where I can't find stuff, or worse, I'm looking at the wrong iteration of something. Oh, and did I mention all the people who have MIME attachment email footers so that figuring out which email contains the document they sent means looking through every single mail? [0]

So I flattened it back down to chronological order and it feels like that restored a lot of sanity.

[0] Obviously a lot of this chaos can be tamed with a more aggressive process for inbox management, but that kind of plays into my point, that's all out of process manual work that a better communication tool should help me with.