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.
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.