After upgrading from Jaguar to Panther, Mail.app ate itself. Every time the client started it froze on a reading mailbox dialog box, no menus were clickable and mail wasn’t being synced. Removing all of my IMAP accounts and rebuilding all of them solved the problem.
No biggie…a small annoyance. But that’s why I rely on IMAP. All my mail is tucked away safe and sound on the server with the tape backup instead of my volatile desktop and notebook systems.