Following my email implosion, I'm seriously considering dropping the native Mac Mail.app and using Thunderbird instead. Apples decision to go with a proprietary mail formal (emlx) rather than the standard mbox format (as an optimization for Spotlight searching) makes me a bit uncomfortable, and the serious Mail.app failure, hiding half my mail for two weeks, leaves me less confident that I can switch when I have to without losing information. Mail and its history is precious stuff.
MacOSXHints points to a converter to generate mbox files from the Apple emlx format.