Mac OSX Leopard will be available soon. Check out the video for a summary of the new features.
For optimum viewing you may want to download the video so you can watch it without transmission delays.
http://www.apple.com/macosx/guidedtour/large.html
Smart data could help you update your address book and the new ichat features make sharing information and remotely controlling a Mac easier.
Here is an article about getting prepared to install Leopard. Be careful about deleting files. When in doubt don’t do it.
http://www.macworld.com/2007/10/secrets/tcoleopardupgrade/index.php