Damaged Fonts -- Lloyd Lim <email@example.com> says that a good check for bad font files, along with other files with resource forks, is to run John Norstad's excellent virus fighter, Disinfectant (now at version 3.2, see below), which checks for and reports damaged resource forks. It may not catch all types of damage, but it is a useful troubleshooting tool.
Fun Way to Send Attachments in Mail
If you're working in a file that you want to attach to a message in Apple Mail, you can transfer the file to Mail easily: From the title bar of the file's window, drag the little proxy icon to Mail's icon on the Dock. Your Mac will make Mail the active application and open a new outgoing message, with the file attached.
(If your icon won't drag, the file probably isn't saved.)