Scott over @ TUAW does something I should have done – point out some of the new security features in Leopard. Check out the full post and Apple's large feature-set listing to get a hint at what's coming our way.

Secure Your Mac: What's new in Leopard security? - The Unofficial Apple Weblog (TUAW): "Apple has a whole section detailing the new security features in Leopard on their huge list of 300+ features to be found in the new OS. The highlights from the security list are:

Tagging downloaded Apps: This feature seems to be what Microsoft was trying to do with Vista. The first time you launch a downloaded app Leopard will ask you if you really want to run this app and display from whence this app came (so if you see it was downloaded for a wacky URL you can cancel launching it).
Application specific firewall: You can set the firewall to allow or refuse connections per app.
Library Randomization: Places system libraries in randomly assigned memory addresses."

(Via TUAW.)