After years and years of sticking with POP because of problems I'd had with IMAP, I'm finally making the switch. Perforce, since accessing my home mail from work is now much more difficult than it's ever been before. (It's totally strange to walk into an office and have there be NO Windows machines anywhere in sight! Possibly in site!)
The first step is converting my three Thunderbird accounts (current, short-term archives, and long-term archives), which are gigabytes of downloaded mail in a couple of hundred mbox files apiece, into Maildir++ trees, and putting them where my equivalent IMAP account(s) can get at 'em. Next, having my incoming mail go to the right place. And finally, sorting all that into the appropriate archive accounts again.
Oh, and arranging for disk space adequate for the task. Which leads to the question:
How the hell do people backup their giga/tera/petabytes of storage these days?