This is the best hint I've come across in a long time. My Mail.app went from frustratingly molasses-slow to amazingly snappy (then again, I've got 4 bloated mailboxes). Go to http://www.hawkwings.net/2007/03/01/a-faster-way-to-speed-up-mailapp/ I kid you not, my Mail app went from a 10-bounce, fifteen second launch time to literally one bounce and -- BAM! -- instant Inbox. Fantastic.