A friend of mine from Apple tipped me off to a cheap-and-easy way of improving the performance of Mail.app, the mailer built into OS X. I've found that every time I send a message, Mail freezes up and the statusbar says, "Adding recipients to Address Book." Turns out that you can really cut down on this delay by forcing your Address Book to compress itself:

1. Open Address Book
2. Create 10 or more entries
3. Delete your new entries
4. Quit Address Book

For extra speedy goodness, try deleting the ~/Library/Application Support/Address Book/ABPerson.index" file, then opening Address Book and searching for an entry. This will force a rebuild of the Address Book index, too.

I've tried it, and it worked beautifully for me. What's more, it seems to have improved the performance of iSync for synching with PalmOS and iPod. Discuss