From the department of So Obvious I Can't Believe I Didn't Do This Earlier...
I'm pretty compulsive about organizing all my mail. On my IMAP account I have about 270 different folders. The folders sit in hierarchies, cataloguing my work and personal life, mailing lists and projects.
Unfortunately when I'm dealing with email this means some time spent trying to find the right place to file each message. Apple's Mail lacks any way to quickly find the folder I want, and I suspect I'm in a minority for being so organized and having this many folders.
Today it occurred to me that I should stop worrying about keeping the hierarchy for my current projects, and file them away when I'm done. This was so stupidly obvious—I do this in real life with paper files—that I can't believe I didn't do it before.
So, may I present my easy-access to current mail folders:
Everything in my current working set now lives in the @CURRENT folder right near the top, meaning minimum time taken to find where to file things.
I share this only in the hope that anyone who is as blind to the obvious as I was might benefit.